In this prospective study, SARS-CoV-2 spike protein specific total immunoglobulin (Ig) levels are analyzed before and after BNT162b2 third mRNA booster vaccination in individuals previously administered with two doses of BBIBP-CorV vaccine in comparison to immunized participants with three doses of BNT162b2 vaccination. Questionnaires from recruited participants are reviewed prior to booster vaccination for the occurrence of a previous SARS-CoV-2 infection and hospitalization.

Sixty-one volunteers (39 females, 22 males) vaccinated by BBIBP-CorV were included with the mean age of 63.9 years. To serve as a control group, 61 patients (41 females, 20 males) were vaccinated with BNT162b2 at a mean age of 59.9 years. At least four months after the first two-dose vaccination regimens, both groups received the third booster BNT162b2 vaccine based on the recommendations of the Hungarian Public Health Centre. Total Ig levels against SARS-CoV-2 spike protein 1 receptor-binding domain (anti-SARS-CoV-2 S1-RBD) were measured by an immunoassay (Roche Diagnostics) and their calculated ratios after/before booster dose were compared between the two groups. Vaccination efficacy via incidence of infection and hospitalization was monitored during study period. We found that BNT162b2 can successfully booster the effect of two-dose BBIBP-CorV vaccination to enhance humoral immune response against SARS-CoV-2 infection.

Inclusion Criteria: -

Exclusion Criteria: included age < 18 years, known primary immunodeficiency, malignancy and ongoing immunosuppressive therapy.

As part of the regular clinical practice, all participants received the third vaccine dose at a general practitioner's (GP) office. Following the initial immunization period, a survey was conducted to monitor vaccine efficacy via the incidence of infection and hospitalization by patient questionnaire. Booster immunization was carried out at least 4 months after the first two doses of basic immunization (two doses of BNT162b2 or BBIBP-CorV), and baseline (pre-booster) antibody level was measured on the same day of the administration of booster immunization (first sampling). Following the booster dose with BNT162b2, another serum sample was collected after 30 days in order to determine induced total level of anti-SARS-CoV-2 spike protein antibodies (second sampling).

These data will be published in a manuscript in a peer-reviewed international journal.