Search

Background: The use of an inactivated severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccine (CoronaVac) against SARS-CoV-2 is implemented worldwide. However, waning immunity and breakthrough infections have been observed. Therefore, we hypothesized that the heterologous booster might improve the protection against the delta and omicron variants.Methods: A total of 224 individuals who completed the 2-dose CoronaVac for 6 months were included. We studied reactogenicity and immunogenicity after a heterologous booster with the inactivated vaccine (BBIBP), the viral vector vaccine (AZD1222), and the messenger ribonucleic acid (mRNA) vaccine (both BNT162B2 and mRNA-1273). We also determined immunogenicity at 3- and 6-month boosting intervals.Results: The solicited adverse events were mild to moderate and well tolerated. Total receptor binding domain (RBD) immunoglobulin (Ig), anti-RBD IgG, focus reduction neutralization test (FRNT50) against delta and omicron variants, and T-cell response were highest in the mRNA-1273 group followed by the BNT162b2, AZD1222, and BBIBP groups, respectively. We also witnessed a higher total Ig anti-RBD in the long-interval than in the short-interval group.Conclusions: All 4 booster vaccines significantly increased binding and neutralizing antibodies in individuals immunized with 2 doses of CoronaVac. The present evidence may benefit vaccine strategies to thwart variants of concern, including the omicron variant. [ABSTRACT FROM AUTHOR]

Graph: Figure 1. class="chapter-para">Neutralizing antibody titers of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) against BA.1 and BA.2 omicron variants at prebooster and 28 days postbooster. These preliminary results indicate that the heterologous booster with mRNA vaccine in AZD1222-primed individuals could induce a robust antibody response that can cross-neutralize both BA.1 and BA.2 omicron variants. To the Editor - In reply to the correspondence from Tjan et al [[1]] regarding the heterologous booster in healthy adults previously immunized with 2 doses of CoronaVac [[2]], the additional knowledge on immunogenicity of the booster (third dose) with BNT162b2 in BNT162b2-primed individuals against the BA.2 omicron variant will help promote the vaccine uptake and coverage in the midst of a surge in BA.2 omicron worldwide. [Extracted from the article]