key: cord-0713792-hg6aivok authors: Vargas Herrera, N. G.; Fernandez-Navarro, M.; Cabezudo-Pillpe, N.; Soto-Becerra, P.; Solis-Sanchez, G.; Escobar-Agreda, S.; Silva-Valencia, J.; Pampa-Espinoza, L.; Bado-Perez, R.; Solari, L.; Araujo-Castillo, R. V. title: Immunogenicity and reactogenicity of a third dose of BNT162b2 vaccine for COVID-19 after a primary regimen with BBIBP-CorV or BNT162b2 vaccines in Lima, Peru. date: 2022-05-03 journal: nan DOI: 10.1101/2022.05.01.22274548 sha: 7f220f67ff3cf9c95a3f135b6bf630c654fe53ab doc_id: 713792 cord_uid: hg6aivok Background: The administration of a third (booster) dose of COVID-19 vaccines in Peru initially employed the BNT162b2 (Pfizer) mRNA vaccine. The national vaccination program started with healthcare workers who received BBIBP-CorV (Sinopharm) vaccine as primary regimen and elderly people previously immunized with BNT162b2. This study evaluated the reactogenicity and immunogenicity of the "booster" dose in these two groups in Lima, Peru. Methods: We conducted a prospective cohort study, recruiting participants from November to December of 2021 in Lima, Peru. We evaluated immunogenicity and reactogenicity in HCW and elderly patients previously vaccinated with either two doses of BBIBP-CorV (heterologous regimen) or BTN162b2 (homologous regimen). Immunogenicity was measured by anti-SARS-CoV-2 IgG antibody levels immediately before boosting dose and 14 days later. IgG geometric means (GM) and medians were obtained, and modeled using ANCOVA and quantile regressions. Results: The GM of IgG levels increased significantly after boosting: from 28.5{+/-}5.0 AU/mL up to 486.6{+/-}1.2 AU/mL (p<0.001) which corresponds to a 17-fold increase. The heterologous vaccine regimen produced higher GM of post-booster anti-SARS-CoV-2 IgG levels, eliciting a 13% fold increase in the geometric mean ratio (95%CI: 1.02-1.27) and a median difference of 92.3 AU/ml (95%CI: 24.9-159.7). Both were safe and well tolerated. Previous COVID-19 infection was also associated with higher pre and post-booster IgG GM levels. Conclusion: Although both boosting regimens were highly immunogenic, two doses of BBIBP-CorV boosted with BTN162b2 produced a stronger IgG antibody response than the homologous BNT162b2 regimen in the Peruvian population. Additionally, both regimens were mildly reactogenic and well-tolerated. The first case of COVID-19 was confirmed in Peru on March 6 th , 2020 (1) . Since then, almost 3,5 79 million COVID-19 cases and more than 200,000 deaths have been reported (2) the immunogenicity/reactogenicity analysis (Figure 1 ). Baseline and demographics characteristics 194 were similar between the group that completed two blood samples and the group lost to follow up 195 (S1 Table) . . CC-BY 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. The copyright holder for this preprint this version posted May 3, 2022. . CC-BY 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. The copyright holder for this preprint this version posted May 3, 2022. (Table 3, Figure 3 ). . CC-BY 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. Figure 2 ). Similar associations were observed when comparisons were 277 performed using medians and IQRs (S3 Table) . . CC-BY 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. The copyright holder for this preprint this version posted May 3, 2022. . CC-BY 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. reported a strong humoral response after a heterologous BNT162b2 booster in HCWs primed with . CC-BY 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. The copyright holder for this preprint this version posted May 3, 2022. is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. The copyright holder for this preprint this version posted May 3, 2022. . CC-BY 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. (which was not certified by peer review) The copyright holder for this preprint this version posted May 3, 2022. ; https://doi.org/10.1101/2022.05.01.22274548 doi: medRxiv preprint In conclusion, two doses of BBIBP-CorV boosted with one BNT162b2 dose elicited very high IgG 394 antibody responses, and three BNT162b2 doses induced a similar response. Both regimens were safe 395 and well tolerated. In addition, the antibody titers rising trend after the second vaccine dose in our 396 study indicates that subsequent boosters could be spaced and prioritized in certain populations such 397 as elderly and immunosuppressed. This reaffirms the importance of mix-and-match strategies that 398 also include inactivated vaccines in order to overcome vaccine availability obstacles. . CC-BY 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. 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