An adverse event (AE) is any untoward medical occurrence in a participant who received study drug without regard to possibility of causal relationship. The TEAEs are defined as events present at baseline that worsened in intensity after administration of study drug or events absent at baseline that emerged after administration of study drug. Solicited AEs are local or systemic predefined events for assessment of reactogenicity. An e-diary was used to collect information on the timing and severity of the solicited AEs. Local AEs included pain, redness/erythema, tenderness, induration/swelling at the site of the injection. Systemic AEs included fever (> 100 °F/37.8 °C), chills, muscle pains, fatigue, headache, malaise, nausea, and vomiting.

Seronegative safety analysis set included all participants who received at least 1 dose of study treatment, were analysed according to treatment actually received, and were seronegative at baseline. Here, number of participants analyzed denotes those participants who were evaluated for solicited symptoms.

The AEs other than solicited AEs are reported as unsolicited AEs and were collected by "open question" at study visits. AE: any untoward medical occurrence in participant who received study drug without regard to possibility of causal relationship. TEAEs: events present at baseline that worsened in intensity after administration of study drug or events absent at baseline that emerged after administration of study drug. SAE: an AE resulting in any of following outcomes or deemed significant for any other reason: death; initial or prolonged inpatient hospitalization; life threatening experience; persistent or significant disability/incapacity; congenital anomaly. MAAE: an AE leading to a non-routine/unscheduled medically-attended visit, to or from medical doctor for any reason. AESI: an event of scientific and medical interest specific to further understanding of study drug safety profile and require close monitoring and rapid communication by investigators to Sponsor.

Seronegative safety analysis set included all participants who received at least 1 dose of study treatment, were analysed according to treatment actually received, and were seronegative at baseline.

Number of participants with abnormal laboratory parameters reported as TEAEs are reported. Laboratory tests included haematology and clinical chemistry.

Seronegative safety analysis set included all participants who received at least 1 dose of study treatment, were analysed according to treatment actually received, and were seronegative at baseline.

Severe acute respiratory syndrome-coronavirus-2 (SARS-CoV-2) nAb were measured by pseudoneutralisation assay. The GMT was calculated as the antilogarithm of Σ(log base 2 transformed titre/n), i.e. as the anti-logarithm transformation of the mean of the log-transformed titre, where 'n' was the number of participants with titre information. Primary Vaccination Cohort:- AZD2816 (4) with response against B.1.351 variant is the comparator group and Primary Vaccination Cohort:- AZD1222 (4) with response against the original Wuhan-Hu-1 strain is the reference group.

Seronegative immunogenicity analysis set: all participants who received at least 1 dose of study treatment, had baseline and post-dose antibody measurements, at least 1 post-dose quantifiable serum titre, and no protocol deviations judged to have potential to interfere with the antibody response, were analysed according to treatment actually received, and were seronegative at baseline. The number of participants analyzed denotes those participants who were evaluable at the specified time frame.

Severe acute respiratory syndrome-coronavirus-2 nAb were measured by pseudoneutralisation assay. The GMT was calculated as the antilogarithm of Σ(log base 2 transformed titre/n), i.e. as the anti-logarithm transformation of the mean of the log-transformed titre, where 'n' was the number of participants with titre information. Booster Cohort:- AZD1222:AZD1222 is the comparator group and AZD1222 in Historical Control is the reference group, both compared for response against the original Wuhan-Hu-1 strain.

Seronegative immunogenicity analysis set: all participants who received at least 1 dose of study treatment, had baseline and post-dose antibody measurements, at least 1 post-dose quantifiable serum titre, and no protocol deviations judged to have potential to interfere with the antibody response, were analysed according to treatment actually received, and were seronegative at baseline. The number of participants analyzed denotes those participants who were evaluable at the specified time frame.

Severe acute respiratory syndrome-coronavirus-2 nAb were measured by pseudoneutralisation assay. Seroresponse was defined as >= 4-fold increase in the GMT of nAb from baseline. Primary Vaccination Cohort:- AZD2816 (4) with response against B.1.351 variant is the comparator group and Primary Vaccination Cohort:- AZD1222 (4) with response against the original Wuhan-Hu-1 strain is the reference group.

Seronegative immunogenicity analysis set: all participants who received at least 1 dose of study treatment, had baseline and post-dose antibody measurements, at least 1 post-dose quantifiable serum titre, and no protocol deviations judged to have potential to interfere with the antibody response, were analysed according to treatment actually received, and were seronegative at baseline. The number of participants analyzed denotes those participants who were evaluable at the specified time frame.

Severe acute respiratory syndrome-coronavirus-2 nAb were measured by pseudoneutralisation assay. The GMT was calculated as the antilogarithm of Σ(log base 2 transformed titre/n), i.e. as the anti-logarithm transformation of the mean of the log-transformed titre, where 'n' was the number of participants with titre information. Booster Cohort:- mRNA:AZD1222 is the comparator group and AZD1222 in Historical Control is the reference group, both compared for response against the original Wuhan-Hu-1 strain.

Seronegative immunogenicity analysis set: all participants who received at least 1 dose of study treatment, had baseline and post-dose antibody measurements, at least 1 post-dose quantifiable serum titre, and no protocol deviations judged to have potential to interfere with the antibody response, were analysed according to treatment actually received, and were seronegative at baseline. The number of participants analyzed denotes those participants who were evaluable at the specified time frame.

An AE is any untoward medical occurrence in a participant who received study drug without regard to possibility of causal relationship. The TEAEs are defined as events present at baseline that worsened in intensity after administration of study drug or events absent at baseline that emerged after administration of study drug. Solicited AEs are local or systemic predefined events for assessment of reactogenicity. An e-diary was used to collect information on the timing and severity of the solicited AEs. Local AEs included pain, redness/erythema, tenderness, induration/swelling at the site of the injection. Systemic AEs included fever (> 100 °F/37.8 °C), chills, muscle pains, fatigue, headache, malaise, nausea, and vomiting.

Seronegative safety analysis set included all participants who received at least 1 dose of study treatment, were analysed according to treatment actually received, and were seronegative at baseline. Here, number of participants analyzed denotes those participants who were evaluated for solicited symptoms.

The AEs other than solicited AEs are reported as unsolicited AEs and were collected by "open question" at study visits. AE: any untoward medical occurrence in participant who received study drug without regard to possibility of causal relationship. TEAEs: events present at baseline that worsened in intensity after administration of study drug or events absent at baseline that emerged after administration of study drug. SAE: an AE resulting in any of following outcomes or deemed significant for any other reason: death; initial or prolonged inpatient hospitalization; life threatening experience; persistent or significant disability/incapacity; congenital anomaly. MAAE: an AE leading to a non-routine/unscheduled medically-attended visit, to or from medical doctor for any reason. AESI: an event of scientific and medical interest specific to further understanding of study drug safety profile and require close monitoring and rapid communication by investigators to Sponsor.

Seronegative safety analysis set included all participants who received at least 1 dose of study treatment, were analysed according to treatment actually received, and were seronegative at baseline.

Severe acute respiratory syndrome-coronavirus-2 nAb were measured by pseudoneutralisation assay. The GMT was calculated as the antilogarithm of Σ(log base 2 transformed titre/n), i.e. as the anti-logarithm transformation of the mean of the log-transformed titre, where 'n' was the number of participants with titre information. Primary Vaccination Cohort:- AZD2816 (4) is the comparator group and Primary Vaccination Cohort:- AZD1222 (4) is the reference group, both compared for response against B.1.351 variant.

Seronegative immunogenicity analysis set: all participants who received at least 1 dose of study treatment, had baseline and post-dose antibody measurements, at least 1 post-dose quantifiable serum titre, and no protocol deviations judged to have potential to interfere with the antibody response, were analysed according to treatment actually received, and were seronegative at baseline. The number of participants analyzed denotes those participants who were evaluable at the specified time frame.

Severe acute respiratory syndrome-coronavirus-2 nAb were measured by pseudoneutralisation assay. The GMT was calculated as the antilogarithm of Σ(log base 2 transformed titre/n), i.e. as the anti-logarithm transformation of the mean of the log-transformed titre, where 'n' was the number of participants with titre information. Primary Vaccination Cohort:- AZD1222 + AZD2816 (4) with response against B.1.351 variant is the comparator group and Primary Vaccination Cohort:- AZD1222 (4) with response against the original Wuhan-Hu-1 strain is the reference group.

Seronegative immunogenicity analysis set: all participants who received at least 1 dose of study treatment, had baseline and post-dose antibody measurements, at least 1 post-dose quantifiable serum titre, and no protocol deviations judged to have potential to interfere with the antibody response, were analysed according to treatment actually received, and were seronegative at baseline. The number of participants analyzed denotes those participants who were evaluable at the specified time frame.

Severe acute respiratory syndrome-coronavirus-2 nAb were measured by pseudoneutralisation assay. The GMT was calculated as the antilogarithm of Σ(log base 2 transformed titre/n), i.e. as the anti-logarithm transformation of the mean of the log-transformed titre, where 'n' was the number of participants with titre information. Primary Vaccination Cohort:- AZD2816 (4) is the comparator group and Primary Vaccination Cohort:- AZD1222 (4) is the reference group, both compared for response against the original Wuhan-Hu-1 strain.

Seronegative immunogenicity analysis set: all participants who received at least 1 dose of study treatment, had baseline and post-dose antibody measurements, at least 1 post-dose quantifiable serum titre, and no protocol deviations judged to have potential to interfere with the antibody response, were analysed according to treatment actually received, and were seronegative at baseline. The number of participants analyzed denotes those participants who were evaluable at the specified time frame.

Severe acute respiratory syndrome-coronavirus-2 nAb were measured by pseudoneutralisation assay. The GMT was calculated as the antilogarithm of Σ(log base 2 transformed titre/n), i.e. as the anti-logarithm transformation of the mean of the log-transformed titre, where 'n' was the number of participants with titre information. Booster Cohort:- AZD1222:AZD2816 with response against B.1.351 variant is the comparator group and AZD1222 in Historical Control with response against the original Wuhan-Hu-1 strain is the reference group.

Seronegative immunogenicity analysis set: all participants who received at least 1 dose of study treatment, had baseline and post-dose antibody measurements, at least 1 post-dose quantifiable serum titre, and no protocol deviations judged to have potential to interfere with the antibody response, were analysed according to treatment actually received, and were seronegative at baseline. The number of participants analyzed denotes those participants who were evaluable at the specified time frame.

Severe acute respiratory syndrome-coronavirus-2 nAb were measured by pseudoneutralisation assay. The GMT was calculated as the antilogarithm of Σ(log base 2 transformed titre/n), i.e. as the anti-logarithm transformation of the mean of the log-transformed titre, where 'n' was the number of participants with titre information. Booster Cohort:- AZD1222:AZD2816 is the comparator group and Booster Cohort:- AZD1222:AZD1222 is the reference group, both compared for response against B.1.351 variant.

Seronegative immunogenicity analysis set: all participants who received at least 1 dose of study treatment, had baseline and post-dose antibody measurements, at least 1 post-dose quantifiable serum titre, and no protocol deviations judged to have potential to interfere with the antibody response, were analysed according to treatment actually received, and were seronegative at baseline. The number of participants analyzed denotes those participants who were evaluable at the specified time frame.

Severe acute respiratory syndrome-coronavirus-2 nAb were measured by pseudoneutralisation assay. The GMT was calculated as the antilogarithm of Σ(log base 2 transformed titre/n), i.e. as the anti-logarithm transformation of the mean of the log-transformed titre, where 'n' was the number of participants with titre information. Booster Cohort:- AZD1222:AZD2816 is the comparator group and AZD1222 in Historical Control is the reference group, both compared for response against the original Wuhan-Hu-1 strain.

Seronegative immunogenicity analysis set: all participants who received at least 1 dose of study treatment, had baseline and post-dose antibody measurements, at least 1 post-dose quantifiable serum titre, and no protocol deviations judged to have potential to interfere with the antibody response, were analysed according to treatment actually received, and were seronegative at baseline. The number of participants analyzed denotes those participants who were evaluable at the specified time frame.

Severe acute respiratory syndrome-coronavirus-2 nAb were measured by pseudoneutralisation assay. The GMT was calculated as the antilogarithm of Σ(log base 2 transformed titre/n), i.e. as the anti-logarithm transformation of the mean of the log-transformed titre, where 'n' was the number of participants with titre information. Booster Cohort:- AZD1222:AZD2816 is the comparator group and Booster Cohort:- AZD1222:AZD1222 is the reference group, both compared for response against the original Wuhan-Hu-1 strain.

Seronegative immunogenicity analysis set: all participants who received at least 1 dose of study treatment, had baseline and post-dose antibody measurements, at least 1 post-dose quantifiable serum titre, and no protocol deviations judged to have potential to interfere with the antibody response, were analysed according to treatment actually received, and were seronegative at baseline. The number of participants analyzed denotes those participants who were evaluable at the specified time frame.

Severe acute respiratory syndrome-coronavirus-2 nAb were measured by pseudoneutralisation assay. The GMT was calculated as the antilogarithm of Σ(log base 2 transformed titre/n), i.e. as the anti-logarithm transformation of the mean of the log-transformed titre, where 'n' was the number of participants with titre information. Booster Cohort:- AZD1222:AZD2816 is the comparator group and Primary Vaccination Cohort:- AZD1222 (4) is the reference group, both compared for response against B.1.351 variant.

Seronegative immunogenicity analysis set: all participants who received at least 1 dose of study treatment, had baseline and post-dose antibody measurements, at least 1 post-dose quantifiable serum titre, and no protocol deviations judged to have potential to interfere with the antibody response, were analysed according to treatment actually received, and were seronegative at baseline. The number of participants analyzed denotes those participants who were evaluable at the specified time frame.

Severe acute respiratory syndrome-coronavirus-2 nAb were measured by pseudoneutralisation assay. The GMT was calculated as the antilogarithm of Σ(log base 2 transformed titre/n), i.e. as the anti-logarithm transformation of the mean of the log-transformed titre, where 'n' was the number of participants with titre information. Booster Cohort:- mRNA:AZD2816 with response against B.1.351 variant is the comparator group and AZD1222 in Historical Control with response against the original Wuhan-Hu-1 strain is the reference group.

Seronegative immunogenicity analysis set: all participants who received at least 1 dose of study treatment, had baseline and post-dose antibody measurements, at least 1 post-dose quantifiable serum titre, and no protocol deviations judged to have potential to interfere with the antibody response, were analysed according to treatment actually received, and were seronegative at baseline. The number of participants analyzed denotes those participants who were evaluable at the specified time frame.

Severe acute respiratory syndrome-coronavirus-2 nAb were measured by pseudoneutralisation assay. The GMT was calculated as the antilogarithm of Σ(log base 2 transformed titre/n), i.e. as the anti-logarithm transformation of the mean of the log-transformed titre, where 'n' was the number of participants with titre information. Booster Cohort:- mRNA:AZD2816 is the comparator group and Booster Cohort:- mRNA:AZD1222 is the reference group, both compared for response against B.1.351 variant.

Seronegative immunogenicity analysis set: all participants who received at least 1 dose of study treatment, had baseline and post-dose antibody measurements, at least 1 post-dose quantifiable serum titre, and no protocol deviations judged to have potential to interfere with the antibody response, were analysed according to treatment actually received, and were seronegative at baseline. The number of participants analyzed denotes those participants who were evaluable at the specified time frame.

Severe acute respiratory syndrome-coronavirus-2 nAb were measured by pseudoneutralisation assay. The GMT was calculated as the antilogarithm of Σ(log base 2 transformed titre/n), i.e. as the anti-logarithm transformation of the mean of the log-transformed titre, where 'n' was the number of participants with titre information. Booster Cohort:- mRNA:AZD2816 is the comparator group and AZD1222 in Historical Control is the reference group, both compared for response against the original Wuhan-Hu-1 strain.

Seronegative immunogenicity analysis set: all participants who received at least 1 dose of study treatment, had baseline and post-dose antibody measurements, at least 1 post-dose quantifiable serum titre, and no protocol deviations judged to have potential to interfere with the antibody response, were analysed according to treatment actually received, and were seronegative at baseline. The number of participants analyzed denotes those participants who were evaluable at the specified time frame.

Severe acute respiratory syndrome-coronavirus-2 nAb were measured by pseudoneutralisation assay. The GMT was calculated as the antilogarithm of Σ(log base 2 transformed titre/n), i.e. as the anti-logarithm transformation of the mean of the log-transformed titre, where 'n' was the number of participants with titre information. Booster Cohort:- mRNA:AZD2816 is the comparator group and Booster Cohort:- mRNA:AZD1222 is the reference group, both compared for response against the original Wuhan-Hu-1 strain.

Seronegative immunogenicity analysis set: all participants who received at least 1 dose of study treatment, had baseline and post-dose antibody measurements, at least 1 post-dose quantifiable serum titre, and no protocol deviations judged to have potential to interfere with the antibody response, were analysed according to treatment actually received, and were seronegative at baseline. The number of participants analyzed denotes those participants who were evaluable at the specified time frame.

Severe acute respiratory syndrome-coronavirus-2 nAb were measured by pseudoneutralisation assay. The GMT was calculated as the antilogarithm of Σ(log base 2 transformed titre/n), i.e. as the anti-logarithm transformation of the mean of the log-transformed titre, where 'n' was the number of participants with titre information. Booster Cohort:- mRNA:AZD2816 is the comparator group and Primary Vaccination Cohort:- AZD1222 (4) is the reference group, both compared for response against B.1.351 variant.

Seronegative immunogenicity analysis set: all participants who received at least 1 dose of study treatment, had baseline and post-dose antibody measurements, at least 1 post-dose quantifiable serum titre, and no protocol deviations judged to have potential to interfere with the antibody response, were analysed according to treatment actually received, and were seronegative at baseline. The number of participants analyzed denotes those participants who were evaluable at the specified time frame.

Severe acute respiratory syndrome-coronavirus-2 nAb were measured by pseudoneutralisation assay. Seroresponse was defined as >= 4-fold increase in the GMT of nAb from baseline. Booster Cohort:- AZD1222:AZD2816 with response against B.1.351 variant is the comparator group and AZD1222 in Historical Control with response against the original Wuhan-Hu-1 strain is the reference group.

Seronegative immunogenicity analysis set: all participants who received at least 1 dose of study treatment, had baseline and post-dose antibody measurements, at least 1 post-dose quantifiable serum titre, and no protocol deviations judged to have potential to interfere with the antibody response, were analysed according to treatment actually received, and were seronegative at baseline. The number of participants analyzed denotes those participants who were evaluable at the specified time frame.

Severe acute respiratory syndrome-coronavirus-2 nAb were measured by pseudoneutralisation assay. Seroresponse was defined as >= 4-fold increase in the GMT of nAb from baseline. Booster Cohort:- AZD1222:AZD2816 is the comparator group and Booster Cohort:- AZD1222:AZD1222 is the reference group, both compared for response against B.1.351 variant.

Seronegative immunogenicity analysis set: all participants who received at least 1 dose of study treatment, had baseline and post-dose antibody measurements, at least 1 post-dose quantifiable serum titre, and no protocol deviations judged to have potential to interfere with the antibody response, were analysed according to treatment actually received, and were seronegative at baseline. The number of participants analyzed denotes those participants who were evaluable at the specified time frame.

Severe acute respiratory syndrome-coronavirus-2 nAb were measured by pseudoneutralisation assay. Seroresponse was defined as >= 4-fold increase in the GMT of nAb from baseline. Booster Cohort:- AZD1222:AZD2816 is the comparator group and AZD1222 in Historical Control is the reference group, both compared for response against the original Wuhan-Hu-1 strain.

Seronegative immunogenicity analysis set: all participants who received at least 1 dose of study treatment, had baseline and post-dose antibody measurements, at least 1 post-dose quantifiable serum titre, and no protocol deviations judged to have potential to interfere with the antibody response, were analysed according to treatment actually received, and were seronegative at baseline. The number of participants analyzed denotes those participants who were evaluable at the specified time frame.

Severe acute respiratory syndrome-coronavirus-2 nAb were measured by pseudoneutralisation assay. Seroresponse was defined as >= 4-fold increase in the GMT of nAb from baseline. Booster Cohort:- AZD1222:AZD2816 is the comparator group and Booster Cohort:- AZD1222:AZD1222 is the reference group, both compared for response against the original Wuhan-Hu-1 strain.

Seronegative immunogenicity analysis set: all participants who received at least 1 dose of study treatment, had baseline and post-dose antibody measurements, at least 1 post-dose quantifiable serum titre, and no protocol deviations judged to have potential to interfere with the antibody response, were analysed according to treatment actually received, and were seronegative at baseline. The number of participants analyzed denotes those participants who were evaluable at the specified time frame.

Severe acute respiratory syndrome-coronavirus-2 nAb were measured by pseudoneutralisation assay. Seroresponse was defined as >= 4-fold increase in the GMT of nAb from baseline. Booster Cohort:- AZD1222:AZD2816 is the comparator group and Primary Vaccination Cohort:- AZD1222 (4) is the reference group, both compared for response against B.1.351 variant.

Seronegative immunogenicity analysis set: all participants who received at least 1 dose of study treatment, had baseline and post-dose antibody measurements, at least 1 post-dose quantifiable serum titre, and no protocol deviations judged to have potential to interfere with the antibody response, were analysed according to treatment actually received, and were seronegative at baseline. The number of participants analyzed denotes those participants who were evaluable at the specified time frame.

Severe acute respiratory syndrome-coronavirus-2 nAb were measured by pseudoneutralisation assay. Seroresponse was defined as >= 4-fold increase in the GMT of nAb from baseline. Booster Cohort:- mRNA:AZD2816 with response against B.1.351 variant is the comparator group and AZD1222 in Historical Control with response against the original Wuhan-Hu-1 strain is the reference group.

Seronegative immunogenicity analysis set: all participants who received at least 1 dose of study treatment, had baseline and post-dose antibody measurements, at least 1 post-dose quantifiable serum titre, and no protocol deviations judged to have potential to interfere with the antibody response, were analysed according to treatment actually received, and were seronegative at baseline. The number of participants analyzed denotes those participants who were evaluable at the specified time frame.

Severe acute respiratory syndrome-coronavirus-2 nAb were measured by pseudoneutralisation assay. Seroresponse was defined as >= 4-fold increase in the GMT of nAb from baseline. Booster Cohort:- mRNA:AZD2816 is the comparator group and Booster Cohort:- mRNA:AZD1222 is the reference group, both compared for response against B.1.351 variant.

Seronegative immunogenicity analysis set: all participants who received at least 1 dose of study treatment, had baseline and post-dose antibody measurements, at least 1 post-dose quantifiable serum titre, and no protocol deviations judged to have potential to interfere with the antibody response, were analysed according to treatment actually received, and were seronegative at baseline. The number of participants analyzed denotes those participants who were evaluable at the specified time frame.

Severe acute respiratory syndrome-coronavirus-2 nAb were measured by pseudoneutralisation assay. Seroresponse was defined as >= 4-fold increase in the GMT of nAb from baseline. Booster Cohort:- mRNA:AZD2816 is the comparator group and AZD1222 in Historical Control is the reference group, both compared for response against the original Wuhan-Hu-1 strain.

Seronegative immunogenicity analysis set: all participants who received at least 1 dose of study treatment, had baseline and post-dose antibody measurements, at least 1 post-dose quantifiable serum titre, and no protocol deviations judged to have potential to interfere with the antibody response, were analysed according to treatment actually received, and were seronegative at baseline. The number of participants analyzed denotes those participants who were evaluable at the specified time frame.

Severe acute respiratory syndrome-coronavirus-2 nAb were measured by pseudoneutralisation assay. Seroresponse was defined as >= 4-fold increase in the GMT of nAb from baseline. Booster Cohort:- mRNA:AZD2816 is the comparator group and Booster Cohort:- mRNA:AZD1222 is the reference group, both compared for response against the original Wuhan-Hu-1 strain.

Seronegative immunogenicity analysis set: all participants who received at least 1 dose of study treatment, had baseline and post-dose antibody measurements, at least 1 post-dose quantifiable serum titre, and no protocol deviations judged to have potential to interfere with the antibody response, were analysed according to treatment actually received, and were seronegative at baseline. The number of participants analyzed denotes those participants who were evaluable at the specified time frame.

Severe acute respiratory syndrome-coronavirus-2 nAb were measured by pseudoneutralisation assay. Seroresponse was defined as >= 4-fold increase in the GMT of nAb from baseline. Booster Cohort:- mRNA:AZD2816 is the comparator group and Primary Vaccination Cohort:- AZD1222 (4) is the reference group, both compared for response against B.1.351 variant.

Seronegative immunogenicity analysis set: all participants who received at least 1 dose of study treatment, had baseline and post-dose antibody measurements, at least 1 post-dose quantifiable serum titre, and no protocol deviations judged to have potential to interfere with the antibody response, were analysed according to treatment actually received, and were seronegative at baseline. The number of participants analyzed denotes those participants who were evaluable at the specified time frame.

An AE is any untoward medical occurrence in a participant who received study drug without regard to possibility of causal relationship. An SAE is an AE resulting in any of the following outcomes or deemed significant for any other reason: death; initial or prolonged inpatient hospitalization; life threatening experience (immediate risk of dying); persistent or significant disability/incapacity; congenital anomaly. The TEAEs are defined as events present at baseline that worsened in intensity after administration of study drug or events absent at baseline that emerged after administration of study drug. The MAAEs are defined as AEs leading to medically-attended visits that were not routine visits, or an otherwise unscheduled visit to or from medical doctor for any reason. The AESIs are events of scientific and medical interest specific to the further understanding of study drug safety profile and require close monitoring and rapid communication by the investigators to the Sponsor.

Seronegative safety analysis set included all participants who received at least 1 dose of study treatment, were analysed according to treatment actually received, and were seronegative at baseline.

Severe acute respiratory syndrome-coronavirus-2 nAb were measured by pseudoneutralisation assay. The GMT was calculated as the antilogarithm of Σ(log base 2 transformed titre/n), i.e. as the anti-logarithm transformation of the mean of the log-transformed titre, where 'n' was the number of participants with titre information. Primary Vaccination Cohort:- AZD1222 + AZD2816 (4) is the comparator group and Primary Vaccination Cohort:- AZD1222 (4) is the reference group, both compared for response against B.1.351 variant.

Seronegative immunogenicity analysis set: all participants who received at least 1 dose of study treatment, had baseline and post-dose antibody measurements, at least 1 post-dose quantifiable serum titre, and no protocol deviations judged to have potential to interfere with the antibody response, were analysed according to treatment actually received, and were seronegative at baseline. The number of participants analyzed denotes those participants who were evaluable at the specified time frame.

Severe acute respiratory syndrome-coronavirus-2 nAb were measured by pseudoneutralisation assay. The GMT was calculated as the antilogarithm of Σ(log base 2 transformed titre/n), i.e. as the anti-logarithm transformation of the mean of the log-transformed titre, where 'n' was the number of participants with titre information. Primary Vaccination Cohort:- AZD1222 + AZD2816 (4) is the comparator group and Primary Vaccination Cohort:- AZD1222 (4) is the reference group, both compared for response against the Original Wuhan-Hu-1 Strain.

Seronegative immunogenicity analysis set: all participants who received at least 1 dose of study treatment, had baseline and post-dose antibody measurements, at least 1 post-dose quantifiable serum titre, and no protocol deviations judged to have potential to interfere with the antibody response, were analysed according to treatment actually received, and were seronegative at baseline. The number of participants analyzed denotes those participants who were evaluable at the specified time frame.

Severe acute respiratory syndrome-coronavirus-2 nAb were measured by pseudoneutralisation assay. The GMT was calculated as the antilogarithm of Σ(log base 2 transformed titre/n), i.e. as the anti-logarithm transformation of the mean of the log-transformed titre, where 'n' was the number of participants with titre information. Primary Vaccination Cohort:- AZD2816 (4) with response against B.1.351 variant is the comparator group and Primary Vaccination Cohort:- AZD2816 (4) with response against the original Wuhan-Hu-1 strain is the reference group.

Seronegative immunogenicity analysis set: all participants who received at least 1 dose of study treatment, had baseline and post-dose antibody measurements, at least 1 post-dose quantifiable serum titre, and no protocol deviations judged to have potential to interfere with the antibody response, were analysed according to treatment actually received, and were seronegative at baseline. The number of participants analyzed denotes those participants who were evaluable at the specified time frame.

Severe acute respiratory syndrome-coronavirus-2 nAb were measured by pseudoneutralisation assay. The GMT was calculated as the antilogarithm of Σ(log base 2 transformed titre/n), i.e. as the anti-logarithm transformation of the mean of the log-transformed titre, where 'n' was the number of participants with titre information. Primary Vaccination Cohort:- AZD1222 + AZD2816 (4) with response against B.1.351 variant is the comparator group and Primary Vaccination Cohort:- AZD1222 + AZD2816 (4) with response against the original Wuhan-Hu-1 strain is the reference group.

Seronegative immunogenicity analysis set: all participants who received at least 1 dose of study treatment, had baseline and post-dose antibody measurements, at least 1 post-dose quantifiable serum titre, and no protocol deviations judged to have potential to interfere with the antibody response, were analysed according to treatment actually received, and were seronegative at baseline. The number of participants analyzed denotes those participants who were evaluable at the specified time frame.

Severe acute respiratory syndrome-coronavirus-2 nAb were measured by pseudoneutralisation assay. Seroresponse was defined as >= 4-fold increase in the GMT of nAb from baseline. Primary Vaccination Cohort:- AZD2816 (4) is the comparator group and Primary Vaccination Cohort:- AZD1222 (4) is the reference group, both compared for response against B.1.351 variant.

Seronegative immunogenicity analysis set: all participants who received at least 1 dose of study treatment, had baseline and post-dose antibody measurements, at least 1 post-dose quantifiable serum titre, and no protocol deviations judged to have potential to interfere with the antibody response, were analysed according to treatment actually received, and were seronegative at baseline. The number of participants analyzed denotes those participants who were evaluable at the specified time frame.

Severe acute respiratory syndrome-coronavirus-2 nAb were measured by pseudoneutralisation assay. Seroresponse was defined as >= 4-fold increase in the GMT of nAb from baseline. Primary Vaccination Cohort:- AZD2816 (4) is the comparator group and Primary Vaccination Cohort:- AZD1222 (4) is the reference group, both compared for response against the original Wuhan-Hu-1 strain.

Seronegative immunogenicity analysis set: all participants who received at least 1 dose of study treatment, had baseline and post-dose antibody measurements, at least 1 post-dose quantifiable serum titre, and no protocol deviations judged to have potential to interfere with the antibody response, were analysed according to treatment actually received, and were seronegative at baseline. The number of participants analyzed denotes those participants who were evaluable at the specified time frame.

Severe acute respiratory syndrome-coronavirus-2 nAb were measured by pseudoneutralisation assay. Seroresponse was defined as >= 4-fold increase in the GMT of nAb from baseline. Primary Vaccination Cohort:- AZD1222 + AZD2816 (4) with response against B.1.351 variant is the comparator group and Primary Vaccination Cohort:- AZD1222 (4) with response against the original Wuhan-Hu-1 strain is the reference group.

Seronegative immunogenicity analysis set: all participants who received at least 1 dose of study treatment, had baseline and post-dose antibody measurements, at least 1 post-dose quantifiable serum titre, and no protocol deviations judged to have potential to interfere with the antibody response, were analysed according to treatment actually received, and were seronegative at baseline. The number of participants analyzed denotes those participants who were evaluable at the specified time frame.

Severe acute respiratory syndrome-coronavirus-2 nAb were measured by pseudoneutralisation assay. Seroresponse was defined as >= 4-fold increase in the GMT of nAb from baseline. Primary Vaccination Cohort:- AZD1222 + AZD2816 (4) is the comparator group and Primary Vaccination Cohort:- AZD1222 (4) is the reference group, both compared for response against B.1.351 variant.

Seronegative immunogenicity analysis set: all participants who received at least 1 dose of study treatment, had baseline and post-dose antibody measurements, at least 1 post-dose quantifiable serum titre, and no protocol deviations judged to have potential to interfere with the antibody response, were analysed according to treatment actually received, and were seronegative at baseline. The number of participants analyzed denotes those participants who were evaluable at the specified time frame.

Severe acute respiratory syndrome-coronavirus-2 nAb were measured by pseudoneutralisation assay. Seroresponse was defined as >= 4-fold increase in the GMT of nAb from baseline. Primary Vaccination Cohort:- AZD1222 + AZD2816 (4) is the comparator group and Primary Vaccination Cohort:- AZD1222 (4) is the reference group, both compared for response against the original Wuhan-Hu-1 strain.

Seronegative immunogenicity analysis set: all participants who received at least 1 dose of study treatment, had baseline and post-dose antibody measurements, at least 1 post-dose quantifiable serum titre, and no protocol deviations judged to have potential to interfere with the antibody response, were analysed according to treatment actually received, and were seronegative at baseline. The number of participants analyzed denotes those participants who were evaluable at the specified time frame.

Severe acute respiratory syndrome-coronavirus-2 nAb were measured by pseudoneutralisation assay. Seroresponse was defined as >= 4-fold increase in the GMT of nAb from baseline. Primary Vaccination Cohort:- AZD2816 (4) with response against B.1.351 variant is the comparator group and Primary Vaccination Cohort:- AZD2816 (4) with response against the original Wuhan-Hu-1 strain is the reference group.

Seronegative immunogenicity analysis set: all participants who received at least 1 dose of study treatment, had baseline and post-dose antibody measurements, at least 1 post-dose quantifiable serum titre, and no protocol deviations judged to have potential to interfere with the antibody response, were analysed according to treatment actually received, and were seronegative at baseline. The number of participants analyzed denotes those participants who were evaluable at the specified time frame.

Severe acute respiratory syndrome-coronavirus-2 nAb were measured by pseudoneutralisation assay. Seroresponse was defined as >= 4-fold increase in the GMT of nAb from baseline. Primary Vaccination Cohort:- AZD1222 + AZD2816 (4) with response against B.1.351 variant is the comparator group and Primary Vaccination Cohort:- AZD1222 + AZD2816 (4) with response against the original Wuhan-Hu-1 strain is the reference group.

Seronegative immunogenicity analysis set: all participants who received at least 1 dose of study treatment, had baseline and post-dose antibody measurements, at least 1 post-dose quantifiable serum titre, and no protocol deviations judged to have potential to interfere with the antibody response, were analysed according to treatment actually received, and were seronegative at baseline. The number of participants analyzed denotes those participants who were evaluable at the specified time frame.

Severe acute respiratory syndrome-coronavirus-2 nAb were measured by pseudoneutralisation assay. The GMT was calculated as the antilogarithm of Σ(log base 2 transformed titre/n), i.e. as the anti-logarithm transformation of the mean of the log-transformed titre, where 'n' was the number of participants with titre information. Booster Cohort:- AZD1222:AZD1222 is the comparator group and Primary Vaccination Cohort:- AZD1222 (4) is the reference group, both compared for response against B.1.351 variant.

Seronegative immunogenicity analysis set: all participants who received at least 1 dose of study treatment, had baseline and post-dose antibody measurements, at least 1 post-dose quantifiable serum titre, and no protocol deviations judged to have potential to interfere with the antibody response, were analysed according to treatment actually received, and were seronegative at baseline. The number of participants analyzed denotes those participants who were evaluable at the specified time frame.

Severe acute respiratory syndrome-coronavirus-2 nAb were measured by pseudoneutralisation assay. The GMT was calculated as the antilogarithm of Σ(log base 2 transformed titre/n), i.e. as the anti-logarithm transformation of the mean of the log-transformed titre, where 'n' was the number of participants with titre information. Booster Cohort:- AZD1222:AZD1222 with response against B.1.351 variant is the comparator group and AZD1222 in Historical Control with response against the original Wuhan-Hu-1 strain is the reference group.

Seronegative immunogenicity analysis set: all participants who received at least 1 dose of study treatment, had baseline and post-dose antibody measurements, at least 1 post-dose quantifiable serum titre, and no protocol deviations judged to have potential to interfere with the antibody response, were analysed according to treatment actually received, and were seronegative at baseline. The number of participants analyzed denotes those participants who were evaluable at the specified time frame.

Severe acute respiratory syndrome-coronavirus-2 nAb were measured by pseudoneutralisation assay. The GMT was calculated as the antilogarithm of Σ(log base 2 transformed titre/n), i.e. as the anti-logarithm transformation of the mean of the log-transformed titre, where 'n' was the number of participants with titre information. Booster Cohort:- AZD1222:AZD2816 with response against B.1.351 variant is the comparator group and Booster Cohort:- AZD1222:AZD2816 with response against the original Wuhan-Hu-1 strain is the reference group.

Seronegative immunogenicity analysis set: all participants who received at least 1 dose of study treatment, had baseline and post-dose antibody measurements, at least 1 post-dose quantifiable serum titre, and no protocol deviations judged to have potential to interfere with the antibody response, were analysed according to treatment actually received, and were seronegative at baseline. The number of participants analyzed denotes those participants who were evaluable at the specified time frame.

Severe acute respiratory syndrome-coronavirus-2 nAb were measured by pseudoneutralisation assay. The GMT was calculated as the antilogarithm of Σ(log base 2 transformed titre/n), i.e. as the anti-logarithm transformation of the mean of the log-transformed titre, where 'n' was the number of participants with titre information.Booster Cohort:- AZD1222:AZD1222 with response against B.1.351 variant is the comparator group and Booster Cohort:- AZD1222:AZD1222 with response against the original Wuhan-Hu-1 strain is the reference group.

Seronegative immunogenicity analysis set: all participants who received at least 1 dose of study treatment, had baseline and post-dose antibody measurements, at least 1 post-dose quantifiable serum titre, and no protocol deviations judged to have potential to interfere with the antibody response, were analysed according to treatment actually received, and were seronegative at baseline. The number of participants analyzed denotes those participants who were evaluable at the specified time frame.

Severe acute respiratory syndrome-coronavirus-2 nAb were measured by pseudoneutralisation assay. Seroresponse was defined as >= 4-fold increase in the GMT of nAb from baseline. Booster Cohort:- AZD1222:AZD1222 is the comparator group and AZD1222 in Historical Control is the reference group, both compared for response against the original Wuhan-Hu-1 strain.

Seronegative immunogenicity analysis set: all participants who received at least 1 dose of study treatment, had baseline and post-dose antibody measurements, at least 1 post-dose quantifiable serum titre, and no protocol deviations judged to have potential to interfere with the antibody response, were analysed according to treatment actually received, and were seronegative at baseline. The number of participants analyzed denotes those participants who were evaluable at the specified time frame.

Severe acute respiratory syndrome-coronavirus-2 nAb were measured by pseudoneutralisation assay. Seroresponse was defined as >= 4-fold increase in the GMT of nAb from baseline. Booster Cohort:- AZD1222:AZD1222 is the comparator group and Primary Vaccination Cohort:- AZD1222 (4) is the reference group, both compared for response against B.1.351 Variant.

Seronegative immunogenicity analysis set: all participants who received at least 1 dose of study treatment, had baseline and post-dose antibody measurements, at least 1 post-dose quantifiable serum titre, and no protocol deviations judged to have potential to interfere with the antibody response, were analysed according to treatment actually received, and were seronegative at baseline. The number of participants analyzed denotes those participants who were evaluable at the specified time frame.

Severe acute respiratory syndrome-coronavirus-2 nAb were measured by pseudoneutralisation assay. Seroresponse was defined as >= 4-fold increase in the GMT of nAb from baseline. Booster Cohort:- AZD1222:AZD1222 with response against B.1.351 variant is the comparator group and AZD1222 in Historical Control with response against the original Wuhan-Hu-1 strain is the reference group.

Seronegative immunogenicity analysis set: all participants who received at least 1 dose of study treatment, had baseline and post-dose antibody measurements, at least 1 post-dose quantifiable serum titre, and no protocol deviations judged to have potential to interfere with the antibody response, were analysed according to treatment actually received, and were seronegative at baseline. The number of participants analyzed denotes those participants who were evaluable at the specified time frame.

Severe acute respiratory syndrome-coronavirus-2 nAb were measured by pseudoneutralisation assay. Seroresponse was defined as >= 4-fold increase in the GMT of nAb from baseline. Booster Cohort:- AZD1222:AZD2816 with response against B.1.351 variant is the comparator group and Booster Cohort:- AZD1222:AZD2816 with response against the original Wuhan-Hu-1 strain is the reference group.

Seronegative immunogenicity analysis set: all participants who received at least 1 dose of study treatment, had baseline and post-dose antibody measurements, at least 1 post-dose quantifiable serum titre, and no protocol deviations judged to have potential to interfere with the antibody response, were analysed according to treatment actually received, and were seronegative at baseline. The number of participants analyzed denotes those participants who were evaluable at the specified time frame.

Severe acute respiratory syndrome-coronavirus-2 nAb were measured by pseudoneutralisation assay. Seroresponse was defined as >= 4-fold increase in the GMT of nAb from baseline. Booster Cohort:- AZD1222:AZD1222 with response against B.1.351 variant is the comparator group and Booster Cohort:- AZD1222:AZD1222 with response against the original Wuhan-Hu-1 strain is the reference group.

Seronegative immunogenicity analysis set: all participants who received at least 1 dose of study treatment, had baseline and post-dose antibody measurements, at least 1 post-dose quantifiable serum titre, and no protocol deviations judged to have potential to interfere with the antibody response, were analysed according to treatment actually received, and were seronegative at baseline. The number of participants analyzed denotes those participants who were evaluable at the specified time frame.

Severe acute respiratory syndrome-coronavirus-2 nAb were measured by pseudoneutralisation assay. The GMT was calculated as the antilogarithm of Σ(log base 2 transformed titre/n), i.e. as the anti-logarithm transformation of the mean of the log-transformed titre, where 'n' was the number of participants with titre information. Booster Cohort:- mRNA:AZD1222 is the comparator group and Primary Vaccination Cohort:- AZD1222 (4) is the reference group, both compared for response against B.1.351 variant.

Seronegative immunogenicity analysis set: all participants who received at least 1 dose of study treatment, had baseline and post-dose antibody measurements, at least 1 post-dose quantifiable serum titre, and no protocol deviations judged to have potential to interfere with the antibody response, were analysed according to treatment actually received, and were seronegative at baseline. The number of participants analyzed denotes those participants who were evaluable at the specified time frame.

Severe acute respiratory syndrome-coronavirus-2 nAb were measured by pseudoneutralisation assay. The GMT was calculated as the antilogarithm of Σ(log base 2 transformed titre/n), i.e. as the anti-logarithm transformation of the mean of the log-transformed titre, where 'n' was the number of participants with titre information. Booster Cohort:- mRNA:AZD1222 with response against B.1.351 variant is the comparator group and AZD1222 in Historical Control with response against the original Wuhan-Hu-1 strain is the reference group.

Seronegative immunogenicity analysis set: all participants who received at least 1 dose of study treatment, had baseline and post-dose antibody measurements, at least 1 post-dose quantifiable serum titre, and no protocol deviations judged to have potential to interfere with the antibody response, were analysed according to treatment actually received, and were seronegative at baseline. The number of participants analyzed denotes those participants who were evaluable at the specified time frame.

Severe acute respiratory syndrome-coronavirus-2 nAb were measured by pseudoneutralisation assay. The GMT was calculated as the antilogarithm of Σ(log base 2 transformed titre/n), i.e. as the anti-logarithm transformation of the mean of the log-transformed titre, where 'n' was the number of participants with titre information. Booster Cohort:- mRNA:AZD2816 with response against B.1.351 variant is the comparator group and Booster Cohort:- mRNA:AZD2816 with response against the original Wuhan-Hu-1 strain is the reference group.

Seronegative immunogenicity analysis set: all participants who received at least 1 dose of study treatment, had baseline and post-dose antibody measurements, at least 1 post-dose quantifiable serum titre, and no protocol deviations judged to have potential to interfere with the antibody response, were analysed according to treatment actually received, and were seronegative at baseline. The number of participants analyzed denotes those participants who were evaluable at the specified time frame.

Severe acute respiratory syndrome-coronavirus-2 nAb were measured by pseudoneutralisation assay. The GMT was calculated as the antilogarithm of Σ(log base 2 transformed titre/n), i.e. as the anti-logarithm transformation of the mean of the log-transformed titre, where 'n' was the number of participants with titre information. Booster Cohort:- mRNA:AZD1222 with response against B.1.351 variant is the comparator group and Booster Cohort:- mRNA:AZD1222 with response against the original Wuhan-Hu-1 strain is the reference group.

Seronegative immunogenicity analysis set: all participants who received at least 1 dose of study treatment, had baseline and post-dose antibody measurements, at least 1 post-dose quantifiable serum titre, and no protocol deviations judged to have potential to interfere with the antibody response, were analysed according to treatment actually received, and were seronegative at baseline. The number of participants analyzed denotes those participants who were evaluable at the specified time frame.

Severe acute respiratory syndrome-coronavirus-2 nAb were measured by pseudoneutralisation assay. Seroresponse was defined as >= 4-fold increase in the GMT of nAb from baseline. Booster Cohort:- mRNA:AZD1222 is the comparator group and AZD1222 in Historical Control is the reference group, both compared for response against the original Wuhan-Hu-1 strain.

Seronegative immunogenicity analysis set: all participants who received at least 1 dose of study treatment, had baseline and post-dose antibody measurements, at least 1 post-dose quantifiable serum titre, and no protocol deviations judged to have potential to interfere with the antibody response, were analysed according to treatment actually received, and were seronegative at baseline. The number of participants analyzed denotes those participants who were evaluable at the specified time frame.

Severe acute respiratory syndrome-coronavirus-2 nAb were measured by pseudoneutralisation assay. Seroresponse was defined as >= 4-fold increase in the GMT of nAb from baseline. Booster Cohort:- mRNA:AZD1222 is the comparator group and Primary Vaccination Cohort:- AZD1222 (4) is the reference group, both compared for response against B.1.351 Variant.

Seronegative immunogenicity analysis set: all participants who received at least 1 dose of study treatment, had baseline and post-dose antibody measurements, at least 1 post-dose quantifiable serum titre, and no protocol deviations judged to have potential to interfere with the antibody response, were analysed according to treatment actually received, and were seronegative at baseline. The number of participants analyzed denotes those participants who were evaluable at the specified time frame.

Severe acute respiratory syndrome-coronavirus-2 nAb were measured by pseudoneutralisation assay. Seroresponse was defined as >= 4-fold increase in the GMT of nAb from baseline. Booster Cohort:- mRNA:AZD1222 with response against B.1.351 variant is the comparator group and AZD1222 in Historical Control with response against the original Wuhan-Hu-1 strain is the reference group.

Seronegative immunogenicity analysis set: all participants who received at least 1 dose of study treatment, had baseline and post-dose antibody measurements, at least 1 post-dose quantifiable serum titre, and no protocol deviations judged to have potential to interfere with the antibody response, were analysed according to treatment actually received, and were seronegative at baseline. The number of participants analyzed denotes those participants who were evaluable at the specified time frame.

Severe acute respiratory syndrome-coronavirus-2 nAb were measured by pseudoneutralisation assay. Seroresponse was defined as >= 4-fold increase in the GMT of nAb from baseline. Booster Cohort:- mRNA:AZD2816 with response against B.1.351 variant is the comparator group and Booster Cohort:- mRNA:AZD2816 with response against the original Wuhan-Hu-1 strain is the reference group.

Seronegative immunogenicity analysis set: all participants who received at least 1 dose of study treatment, had baseline and post-dose antibody measurements, at least 1 post-dose quantifiable serum titre, and no protocol deviations judged to have potential to interfere with the antibody response, were analysed according to treatment actually received, and were seronegative at baseline. The number of participants analyzed denotes those participants who were evaluable at the specified time frame.

Severe acute respiratory syndrome-coronavirus-2 nAb were measured by pseudoneutralisation assay. Seroresponse was defined as >= 4-fold increase in the GMT of nAb from baseline. Booster Cohort:- mRNA:AZD1222 with response against B.1.351 variant is the comparator group and Booster Cohort:- mRNA:AZD1222 with response against the original Wuhan-Hu-1 strain is the reference group.

Seronegative immunogenicity analysis set: all participants who received at least 1 dose of study treatment, had baseline and post-dose antibody measurements, at least 1 post-dose quantifiable serum titre, and no protocol deviations judged to have potential to interfere with the antibody response, were analysed according to treatment actually received, and were seronegative at baseline. The number of participants analyzed denotes those participants who were evaluable at the specified time frame.

Severe acute respiratory syndrome-coronavirus-2 nAb were measured by pseudoneutralisation assay. The GMT was calculated as the antilogarithm of Σ(log base 2 transformed titre/n), i.e. as the anti-logarithm transformation of the mean of the log-transformed titre, where 'n' was the number of participants with titre information. Primary Vaccination Cohort:- AZD2816 (4) with response against B.1.351 variant is the comparator group and Primary Vaccination Cohort:- AZD1222 (4) with response against the original Wuhan-Hu-1 strain is the reference group.

Seronegative immunogenicity analysis set: all participants who received at least 1 dose of study treatment, had baseline and post-dose antibody measurements, at least 1 post-dose quantifiable serum titre, and no protocol deviations judged to have potential to interfere with the antibody response, were analysed according to treatment actually received, and were seronegative at baseline. The number of participants analyzed denotes those participants who were evaluable at the specified time frame.

Severe acute respiratory syndrome-coronavirus-2 nAb were measured by pseudoneutralisation assay. The GMT was calculated as the antilogarithm of Σ(log base 2 transformed titre/n), i.e. as the anti-logarithm transformation of the mean of the log-transformed titre, where 'n' was the number of participants with titre information. Primary Vaccination Cohort:- AZD2816 (4) is the comparator group and Primary Vaccination Cohort:- AZD1222 (4) is the reference group, both compared for response against B.1.351 variant.

Seronegative immunogenicity analysis set: all participants who received at least 1 dose of study treatment, had baseline and post-dose antibody measurements, at least 1 post-dose quantifiable serum titre, and no protocol deviations judged to have potential to interfere with the antibody response, were analysed according to treatment actually received, and were seronegative at baseline. The number of participants analyzed denotes those participants who were evaluable at the specified time frame.

Severe acute respiratory syndrome-coronavirus-2 nAb were measured by pseudoneutralisation assay. The GMT was calculated as the antilogarithm of Σ(log base 2 transformed titre/n), i.e. as the anti-logarithm transformation of the mean of the log-transformed titre, where 'n' was the number of participants with titre information. Primary Vaccination Cohort:- AZD1222 + AZD2816 (4) with response against B.1.351 variant is the comparator group and Primary Vaccination Cohort:- AZD1222 (4) with response against the original Wuhan-Hu-1 strain is the reference group.

Seronegative immunogenicity analysis set: all participants who received at least 1 dose of study treatment, had baseline and post-dose antibody measurements, at least 1 post-dose quantifiable serum titre, and no protocol deviations judged to have potential to interfere with the antibody response, were analysed according to treatment actually received, and were seronegative at baseline. The number of participants analyzed denotes those participants who were evaluable at the specified time frame.

Severe acute respiratory syndrome-coronavirus-2 nAb were measured by pseudoneutralisation assay. The GMT was calculated as the antilogarithm of Σ(log base 2 transformed titre/n), i.e. as the anti-logarithm transformation of the mean of the log-transformed titre, where 'n' was the number of participants with titre information. Primary Vaccination Cohort:- AZD2816 (4) is the comparator group and Primary Vaccination Cohort:- AZD1222 (4) is the reference group, both compared for response against the original Wuhan-Hu-1 strain.

Seronegative immunogenicity analysis set: all participants who received at least 1 dose of study treatment, had baseline and post-dose antibody measurements, at least 1 post-dose quantifiable serum titre, and no protocol deviations judged to have potential to interfere with the antibody response, were analysed according to treatment actually received, and were seronegative at baseline. The number of participants analyzed denotes those participants who were evaluable at the specified time frame.

Chimpanzee adenovirus Ox1 (ChAdOx1) vector nAb were measured by neutralisation assay. The GMT was calculated as the antilogarithm of Σ(log base 2 transformed titre/n), i.e. as the anti-logarithm transformation of the mean of the log-transformed titre, where 'n' was the number of participants with titre information.

Seronegative immunogenicity analysis set: all participants who received at least 1 dose of study treatment, had baseline and post-dose antibody measurements, at least 1 post-dose quantifiable serum titre, and no protocol deviations judged to have potential to interfere with the antibody response, were analysed according to treatment actually received, and were seronegative at baseline. The number of participants analyzed denotes those participants who were evaluable at the specified time frame.

Chimpanzee adenovirus Ox1 vector nAb were measured by neutralisation assay. Seroresponse was defined as >= 4-fold increase in the GMT of nAb from baseline.

Seronegative immunogenicity analysis set: all participants who received at least 1 dose of study treatment, had baseline and post-dose antibody measurements, at least 1 post-dose quantifiable serum titre, and no protocol deviations judged to have potential to interfere with the antibody response, were analysed according to treatment actually received, and were seronegative at baseline. The number of participants analyzed denotes those participants who were evaluable at the specified time frame.

Severe acute respiratory syndrome-coronavirus-2 spike protein binding antibodies were measured by multiplexed immunoassay. The GMT was calculated as the antilogarithm of Σ(log base 2 transformed titre/n), i.e. as the anti-logarithm transformation of the mean of the log-transformed titre, where 'n' was the number of participants with titre information.

Seronegative immunogenicity analysis set: all participants who received at least 1 dose of study treatment, had baseline and post-dose antibody measurements, at least 1 post-dose quantifiable serum titre, and no protocol deviations judged to have potential to interfere with the antibody response, were analysed according to treatment actually received, and were seronegative at baseline. The number of participants analyzed denotes those participants who were evaluable at the specified time frame.

Severe acute respiratory syndrome-coronavirus-2 spike protein binding antibodies were measured by multiplexed immunoassay. Seroresponse was defined as >= 4-fold increase in the GMT of spike protein binding antibodies from baseline.

Seronegative immunogenicity analysis set: all participants who received at least 1 dose of study treatment, had baseline and post-dose antibody measurements, at least 1 post-dose quantifiable serum titre, and no protocol deviations judged to have potential to interfere with the antibody response, were analysed according to treatment actually received, and were seronegative at baseline. The number of participants analyzed denotes those participants who were evaluable at the specified time frame.

Severe acute respiratory syndrome-coronavirus-2 nAb and ChAdOx1 vector nAb were measured by pseudoneutralisation assay. Correlations were based on log2 titre values and assessed by using Spearman rank correlation for all cohorts except Primary Vaccination Cohort:- AZD2816 (12) for which Pearson correlation was used. The correlation coefficient is reported in values from +1 to -1 (+1= perfect association, 0 = no association, and -1= perfect negative association). The closer the correlation coefficient is to zero, weaker the association.

Seronegative immunogenicity analysis set: all participants who received at least 1 dose of study treatment, had baseline and post-dose antibody measurements, at least 1 post-dose quantifiable serum titre, and no protocol deviations judged to have potential to interfere with the antibody response, were analysed according to treatment actually received, and were seronegative at baseline. The number of participants analyzed denotes those participants who were evaluable at the specified time frame.