Safety and immunogenicity of full or half dose of COVID-19 booster vaccine after completion of two-dose inactivated and viral vector vaccines

The solicited adverse events were mild to moderate and well tolerated. Total RBD Ig, anti-RBD IgG, neutralizing antibodies 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. All booster vaccines significantly increased binding and neutralizing antibodies in individuals immunized with 2 doses of CoronaVac. The result benefit vaccine strategies to thwart variants of concern, including omicron variant.