Evidence synthesis and pooled analysis of vaccine effectiveness for COVID-19 mRNA vaccine BNT162b2 as a heterologous booster after inactivated SARS-CoV-2 virus vaccines.

Introduction of primary COVID-19 vaccination has helped reduce severe disease and death caused by SARS-CoV-2 infection. Understanding the protection conferred by heterologous booster regimens informs alternative vaccination strategies that enable programmatic resilience and can catalyze vaccine confidence and coverage. Inactivated SARS-CoV-2 vaccines are among the most widely used vaccines worldwide. This review synthesizes the available evidence identified as of May 26, 2022, on the safety, immunogenicity, and effectiveness of a heterologous BNT162b2 (Pfizer-BioNTech) mRNA vaccine booster dose after an inactivated SARS-CoV-2 vaccine primary series, to help protect against COVID-19. Evidence showed that the heterologous BNT16b2 mRNA vaccine booster enhances immunogenicity and improves vaccine effectiveness against COVID-19, and no new safety concerns were identified with heterologous inactivated primary series with mRNA booster combinations.

Robust SARS-CoV-2 Antibody Responses in Asian COVID-Naïve Subjects 180 Days after Two Doses of BNT162b2 mRNA COVID-19 Vaccine.

BACKGROUND: Subjects with previous COVID-19 have augmented post-vaccination responses. However, the antibody response in COVID-naïve subjects from Southeast Asia is not well known. METHODS: 77 COVID-naïve vaccinees were tested with a full antibody panel [spike antibodies (total (T-Ab), IgG, IgM) and neutralizing antibodies (N-Ab)] pre-vaccination, 10 days after dose 1, and 20/40/60/90/120/150/180 days after dose 2. RESULTS: 10 days after dose 1, 67.6% (48/71)/69.0% (49/71) were T-Ab/IgG positive; only 15.5% (11/71)/14.1% (10/71) were N-Ab/IgM positive. While all (100%) subjects had brisk T-Ab, IgG and N-Ab antibody responses 20 days after complete vaccination, only 79.1% (53/67) were IgM positive. At 180 days (n = 8), T-Ab/IgG/N-Ab were still reactive (lowest T-Ab 186 U/mL, IgG 617 AU/mL, N-Ab 0.39 µg/mL), but IgM was negative in all samples. Spike antibody thresholds of T-Ab 74.1 U/mL (r = 0.95) and IgG 916 AU/mL (r = 0.95) corresponded to N-Ab reactivity (>0.3 µg/mL). Non-linear regression analysis showed that N-Ab would decrease to 0.3 µg/mL by 241 days, whereas T-Ab/IgG would need 470/163 days to reach titers of T-Ab/IgG associated with a N-Ab 0.3 µg/mL (76.4 U/mL and 916 AU/mL respectively). CONCLUSIONS: The antibody responses of T-Ab, IgG and N-Ab remain high and durable even at 180 days. N-Ab titers are expected to remain reactive up to 241 days post-vaccination.