Safety and superior immunogenicity of heterologous boosting with an RBD-based SARS-CoV-2 mRNA vaccine in Chinese adults

Dear Editor, To May 2022,the COVID-19 pandemic has claimed more than 6.28 million lives,with more than 524 million confirmed cases worldwide.The recent emergence of highly transmissible Omicron variant of severe acute respiratory syndrome coronavirus 2(SARS-CoV-2)has triggered another major surge in both confirmed cases and deaths.1 Ten COVID-19 vaccines have been approved by the World Health Organization(WHO)for emergency use,including the two mRNA vaccines,BNT162b2 and mRNA-1273,and two Chinese inactivated vaccines,CoronaVac and BBIBP-CorV.How-ever,the rapid waning of vaccine-induced virus-neutralizing antibody titers and the continuous emergence of variants of concern(VOCs),including Alpha,Beta,Delta and Omicron,have created unprecedented challenges in the eradication of COVID-19 pandemic.2-4