Local reactions included redness, swelling, and pain at the injection site occurring at the BNT162b2 or placebo injection site. Local reactions were recorded by participants in an electronic diary (e-diary). Redness and swelling were measured and recorded in measuring device units. 1 measuring device unit =0.5 centimeter (cm) and graded as mild: greater than (>) 2.0 to 5.0 cm, moderate: >5.0 to 10.0 cm, severe: >10.0 cm, and potentially life threatening (Grade 4): necrosis or exfoliative dermatitis. Pain at injection site was graded as mild: did not interfere with daily activity, moderate: interfered with daily activity, severe: prevented daily activity, and potentially life threatening (Grade 4): emergency room visit or hospitalization for severe pain. Exact 2-sided confidence interval (CI), based on the Clopper and Pearson method was used.

Safety population included all participants who received any of the study intervention. Here, ''Number of participants analyzed'' (N) signifies number of participants evaluable and "Number Analyzed" (n) signifies number of participants evaluable for specified rows for this outcome measure.

Local reactions included redness, swelling, and pain at the injection site occurring at the BNT162b2 or placebo injection site. Local reactions were recorded by participants in an e-diary. Redness and swelling were measured and recorded in measuring device units. 1 measuring device unit =0.5 cm and graded as mild: greater than >2.0 to 5.0 cm, moderate: >5.0 to 10.0 cm, severe: >10.0 cm, and potentially life threatening (Grade 4): necrosis or exfoliative dermatitis. Pain at injection site was graded as mild: did not interfere with daily activity, moderate: interfered with daily activity, severe: prevented daily activity, and potentially life threatening (Grade 4): emergency room visit or hospitalization for severe pain. Exact 2-sided CI, based on the Clopper and Pearson method was used.

Safety population included all participants who received any of the study intervention. Here, "Number of participants analyzed" included participants who received Vaccination 2 and signifies number of participants evaluable for this outcome measure.

Systemic events included fever, fatigue, headache, chills, vomiting, diarrhea, new or worsened muscle pain, and new or worsened joint pain recorded by participants in an e-diary. Fever was defined as temperature: >=38.0 degrees (deg) Celsius (C), and categorized as: >=38.0 to 38.4 deg C, >38.4 to 38.9 deg C, >38.9 to 40.0 deg C, and >40.0 deg C. Fatigue, headache, chills, new or worsened muscle pain, and new or worsened joint pain were graded as mild: did not interfere with activity, moderate: some interference with activity, and severe: prevented daily routine activity. Vomiting graded as mild: 1 to 2 times in 24 hours(h), moderate: >2 times in 24h, severe: required intravenous hydration, and grade 4: emergency room (ER) visit or hospitalization for hypotensive shock. Diarrhea graded as mild: 2 to 3 loose stools in 24h, moderate: 4 to 5 loose stools in 24h, severe: 6 or more loose stools in 24h, and grade 4: ER visit or hospitalization for severe diarrhea.

Safety population included all participants who received any of the study intervention. Here, "Number of participants analyzed" signifies number of participants evaluable and "Number Analyzed" (n) signifies number of participants evaluable for specified rows for this outcome measure.

Systemic events included fever, fatigue, headache, chills, vomiting, diarrhea, new or worsened muscle pain, and new or worsened joint pain recorded by participants in an e-diary. Fever was defined as temperature: >=38.0 deg C, and categorized as: >=38.0 to 38.4 deg C, >38.4 to 38.9 deg C, >38.9 to 40.0 deg C, and >40.0 deg C. Fatigue, headache, chills, new or worsened muscle pain, and new or worsened joint pain were graded as mild: did not interfere with activity, moderate: some interference with activity, and severe: prevented daily routine activity. Vomiting graded as mild: 1 to 2 times in 24h, moderate: >2 times in 24h, severe: required intravenous hydration, and grade 4: ER visit or hospitalization for hypotensive shock. Diarrhea graded as mild: 2 to 3 loose stools in 24h, moderate: 4 to 5 loose stools in 24h, severe: 6 or more loose stools in 24h, and grade 4: ER visit or hospitalization for severe diarrhea. Exact 2-sided CI, based on Clopper and Pearson method used.

Safety population included all participants who received any of the study intervention. Here, "Number of participants analyzed" included participants who received Vaccination 2 and signifies number of participants evaluable for this outcome measure.

An AE was defined as any untoward medical occurrence in a clinical study participant, temporally associated with the use of study intervention, whether or not considered related to the study intervention. Exact 2-sided CI was calculated using the Clopper and Pearson method. Only AEs collected by non-systematic assessment (i.e. excluding local reactions and systemic events) were reported in this outcome measure.

Safety population included all participants who received any of the study intervention.

An AE was defined as any untoward medical occurrence in a clinical study participant, temporally associated with the use of study intervention, whether or not considered related to the study intervention. Exact 2-sided CI was calculated using the Clopper and Pearson method. Only AEs collected by non-systematic assessment (i.e. excluding local reactions and systemic events) were reported in this outcome measure.

Safety population included all participants who received any of the study intervention. Here, "Number of participants analyzed" signifies number of participants evaluable for this outcome measure''.

An AE was defined as any untoward medical occurrence in a clinical study participant, temporally associated with the use of study intervention, whether or not considered related to the study intervention. Exact 2-sided CI was calculated using the Clopper and Pearson method. SAE was an AE resulting in any of the following outcomes or deemed significant for any other reason: death; initial/prolonged inpatient hospitalization; life-threatening experience (immediate risk of dying); persistent or significant disability/incapacity; congenital anomaly; or that was considered to be an important medical event.

Safety population included all participants who received any of the study intervention.

An AE was defined as any untoward medical occurrence in a clinical study participant, temporally associated with the use of study intervention, whether or not considered related to the study intervention. Exact 2-sided CI was calculated using the Clopper and Pearson method. SAE was an AE resulting in any of the following outcomes or deemed significant for any other reason: death; initial/prolonged inpatient hospitalization; life-threatening experience (immediate risk of dying); persistent or significant disability/incapacity; congenital anomaly; or that was considered to be an important medical event.

Safety population included all participants who received any of the study intervention. Here, "Number of participants analyzed" signifies number of participants evaluable for this outcome measure''.

GMCs of full-length S-binding IgG level for the coadministration group and separate administration group were reported in this outcome measure in descriptive data section. GMC and the 2-sided 95% CI were calculated by exponentiating the LSMeans of the concentrations and the corresponding CIs based on analysis of logarithmically transformed assay results using a linear regression model with terms of vaccine group, age group, and the corresponding baseline assay results (log scale). Assay results below the LLOQ were set to 0.5*LLOQ. Geometric mean ratio (GMR) was reported in the statistical analysis section and was calculated as ratio of GMCs in the coadministration group to the separate administration group. Here, "Number of participants analyzed" signifies number of participants evaluable for this outcome measure.

Evaluable BNT162b2 immunogenicity population: Eligible participants who received all vaccinations(Vax) at Visit1(V1) (coadministration group) or all Vax at V1 and V2 (separate administration group) as randomized, had at least 1 valid full-length S-binding IgG result from blood sample collected 28 to 42 days after BNT162b2 vax, had no reported COVID-19/new SARS-CoV-2 infection after V1 through 1 month after BNT162b2 vax, and had no other important protocol deviations as determined by clinician.

GMTs of strain-specific HAI titers for the coadministration group and separate administration group were reported in this outcome measure in descriptive data section. GMTs and the 2-sided 95% CIs were calculated by exponentiating the LSMeans of the titers and the corresponding CIs based on analysis of logarithmically transformed assay results using a linear regression model with terms of vaccine group, age group, and the corresponding baseline assay results (log scale). Assay results below the LLOQ were set to 0.5*LLOQ, and results above the ULOQ were set to ULOQ+1. Geometric mean ratio (GMR) was reported in the statistical analysis section and was calculated as ratio of GMT in the coadministration group to the separate administration group.

Evaluable SIIV immunogenicity population: participants who received all vaccinations at Visit 1 as randomized, had at least 1 valid and determinate HAI titer result from the blood sample collected 28 to 42 days after SIIV, and had no other important protocol deviations as determined by the clinician. Here, "Number of participants analyzed" signifies number of participants evaluable and "Number Analyzed" (n) signifies number of participants evaluable for specified rows for this outcome measure.

GMCs were calculated by exponentiating the mean logarithm of the concentrations and the corresponding CIs (based on the Student's t-distribution). Assay results below the lower limit of quantitation (LLOQ) were set to 0.5*LLOQ. Here, "Number of participants analyzed" signifies number of participants evaluable for this outcome measure''.

Evaluable BNT162b2 immunogenicity population: Eligible participants who received all vaccinations(Vax) at Visit1(V1) (coadministration group) or all Vax at V1 and V2 (separate administration group) as randomized, had at least 1 valid full-length S-binding IgG result from blood sample collected 28 to 42 days after BNT162b2 vax, had no reported COVID-19/new SARS-CoV-2 infection after V1 through 1 month after BNT162b2 vax, and had no other important protocol deviations as determined by clinician.

GMFR was defined as the geometric mean of the ratios of IgG concentrations at 1 month after BNT162b2 vaccination to that before BNT162b2 vaccination. GMFRs were calculated by exponentiating the mean logarithm of fold rises and the corresponding CIs (based on the Student's t-distribution). Assay results below the LLOQ were set to 0.5*LLOQ. Here, "Number of participants analyzed" signifies number of participants evaluable for this outcome measure''.

Evaluable BNT162b2 immunogenicity population: Eligible participants who received all vaccinations(Vax) at Visit1(V1) (coadministration group) or all Vax at V1 and V2 (separate administration group) as randomized, had at least 1 valid full-length S-binding IgG result from blood sample collected 28 to 42 days after BNT162b2 vax, had no reported COVID-19/new SARS-CoV-2 infection after V1 through 1 month after BNT162b2 vax, and had no other important protocol deviations as determined by clinician.

GMTs were calculated by exponentiating the mean logarithm of the titers and the corresponding CIs (based on the Student's t-distribution). Assay results below LLOQ were set to 0.5*LLOQ. Here, "Number of participants analyzed" signifies number of participants evaluable for this outcome measure''. Analysis was performed in a subset of 100 participants from each group.

Evaluable BNT162b2 immunogenicity population: Eligible participants who received all Vax at V1 (coadministration group) or all Vax at V1 and V2 (separate administration group) as randomized, had at least 1 valid SARS-CoV-2 neutralizing titers result from blood sample collected 28 to 42 days after BNT162b2 vax, had no reported COVID-19/new SARS-CoV-2 infection after V1 through 1 month after BNT162b2 vax, and had no other important protocol deviations as determined by clinician.

GMFR was defined as the geometric mean of the ratios of SARS-CoV-2 neutralizing titers at 1 month after BNT162b2 vaccination to that before BNT162b2 vaccination. GMFRs were calculated by exponentiating the mean logarithm of fold rises and the corresponding CIs (based on the Student's t-distribution). Assay results below the LLOQ were set to 0.5*LLOQ. Here, "Number of participants analyzed" signifies number of participants evaluable for this outcome measure''. Analysis was performed in a subset of 100 participants from each group.

Evaluable BNT162b2 immunogenicity population: Eligible participants who received all Vax at V1 (coadministration group) or all Vax at V1 and V2 (separate administration group) as randomized, had at least 1 valid SARS-CoV-2 neutralizing titers result from blood sample collected 28 to 42 days after BNT162b2 vax, had no reported COVID-19/new SARS-CoV-2 infection after V1 through 1 month after BNT162b2 vax, and had no other important protocol deviations as determined by clinician.

GMTs were calculated by exponentiating the mean logarithm of the titers and the corresponding CIs (based on the Student's t-distribution). Assay results below the LLOQ were set to 0.5*LLOQ, and results above the ULOQ were set to ULOQ+1. The analysis was performed on the influenza strains: H1N1 A/Victoria, H3N2 A/Darwin, B/Austria, and B/Phuket.

Evaluable SIIV immunogenicity population: eligible randomized participants who received all vaccinations at Visit 1 as randomized, had at least 1 valid and determinate HAI titer result from the blood sample collected for 28 to 42 days after SIIV vax, and had no other important protocol deviations as determined by the clinician. Here, "N" signifies number of participants evaluable, and "n" signifies number of participants evaluable for specified rows for this outcome measure.

GMFR was defined as ratio of the geometric mean of strain-specific HAI titers at 1 month after SIIV vaccination to the geometric mean of strain-specific HAI titers before SIIV vaccination. GMFRs were calculated by exponentiating the mean logarithm of fold rises and the corresponding CIs (based on the Student's t-distribution). Assay results below the LLOQ were set to 0.5*LLOQ, and results above the ULOQ were set to ULOQ+1. The analysis was performed on the influenza strains: H1N1 A/Victoria, H3N2 A/Darwin, B/Austria, and B/Phuket.

Evaluable SIIV immunogenicity population: eligible randomized participants who received all vaccinations at Visit 1 as randomized, had at least 1 valid and determinate HAI titer result from blood sample collected for 28 to 42 days after SIIV vax, and had no other important protocol deviations as determined by clinician. Here, "N" signifies number of participants evaluable, and "n" signifies number of participants evaluable for specified rows for this outcome measure.