Recombinant protein subunit vaccine booster following two-dose inactivated vaccines dramatically enhanced anti-RBD responses and neutralizing titers against SARS-CoV-2 and Variants of Concern.

Dear Editor, As of October,2021,SARS-CoV-2 has infected more than 230 million people;promoting roll-out vaccinations could help build herd immunity for the pandemic.However,the waning of antibody in magnitude and decreased protective efficacy in multiple types of vaccines have been reported:Along with the circulating variants to some degree escaping from immune response,these led to the argument of further booster vaccination in recipients who have previously received "priming" vaccination.