Discussion
infection
ADVERSE EVENTS, INFECTION, VIRUS
Vaccination provides immune-protection against SARS-CoV-2, owing to the induction of neutralizing antibodies and cellular immunity. However, as we are faced with the rapid evolution of SARS-CoV-2 variants worldwide and the virus’s increasing immune escape abilityThe antibody levels following homologous booster of inactivated vaccine in participants decayed faster than with a heterologous Ad5-nCoV booster. In a study into the use of a third-dose Ad5-nCoV or inactivated vaccine, Jin et al. demonstrated that orally administering aerosolized Ad5-nCoV following two-dose CoronaVac priming was persistently more immunogenic than a third CoronaVac dose 12 months after the second dosePrevious clinical trials reported that most adverse events after Ad5-nCoV were mild or moderate in severity and might be associated with cellular immunity reactivityThe morbidity and mortality rates in older adults increase after infection with SARS-CoV-2, and an effective COVID-19 vaccine is urgently neededThis study had some limitations. First, live virus in vitro neutralization tests against WT SARS-CoV-2 and Omicron BA.4/5 were not conducted in our study, and these need to be further explored, although RBD-specific binding IgG and pseudovirus-neutralizing antibody levels induced by vaccination were shown to correlate with live virus neutralizing antibody levels in our previous studyIn conclusion, our study provided evidence that a fourth dose of Ad5-nCoV following a three-dose inactivated SARS-CoV-2 vaccination is more immunogenic, tolerable than a fourth inactivated SARS-CoV-2 vaccine. Ad5-nCoV elicits a stronger humoral response and restores higher peak and more durable antibody levels than the inactivated SARS-CoV-2 vaccine. Nevertheless, while Ad5-nCoV seems to be highly potent and protective against Omicron lineages, next-generation vaccines may be needed to provide better protection against the emergence of highly transmissible SARS-CoV-2 variants capable of immune escape.