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The immunogenicity and safety of different COVID-19 booster vaccination following CoronaVac or ChAdOx1 nCoV-19 primary series

The appropriate COVID-19 booster vaccine following inactivated or adenoviral vector COVID-19 vaccination is unclear. We evaluated the safety and immunogenicity of different booster vaccines, inactivated (BBIBP-CorV), chimpanzee adenoviral vector (ChAdOx1), or mRNA (BNT162b2 at full (30 g), or half (15 g) dose) in healthy adults who received 2-dose primary series of either inactivated vaccine (CoronaVac) or ChAdOx1 8-12 weeks earlier. Overall, the adverse events for all booster vaccines were mild and moderate. Two weeks post-booster dose, the neutralising antibody titres against Delta variant in CoronaVac-prime and ChAdOx1-prime were highest with for 30g-BNT162b2 (411 vs 470) and 15g-BNT162b2 (499 vs 358); followed by ChAdOx1 (271 vs 69), and BBIBP-CorV (61.3 vs 49). BNT162b2 also induced higher interferon gamma response. Heterologous COVID-19 boosting vaccination with BNT162b2 is the most immunogenic following CoronaVac or ChAdOx1 primary series. A lower dose BNT162b2 may be used as booster in settings with limited vaccine supply.