Abstract:
Immunity against COVID-19 infection in vaccinated individuals varies based on the vaccine type, duration after vaccination or infection, and SARS-CoV-2 variant type. We conducted a observational study to evaluate the immunogenicity of a booster vaccination with AZD1222 after two doses of CoronaVac (booster group) compared to individuals who had COVID-19 infection after receiving two doses of CoronaVac (infection group). We used a surrogate virus neutralization test (sVNT) to evaluate immunity against wild-type and Omicron variant (BA.1) at 3 and 6 months after infection or booster dose. Of the 50 participants, 25 were in the infection group, and 25 were in the booster group. At 3 months post-infection or booster vaccination, the median sVNT against wild-type at 3 months after infection or booster vaccination was 97.87% (IQR 97.78%-97.94%) in the infection group and 97.6% (IQR 94.6%-98%) in the booster group (p=0.21). At 6 months, the median sVNT against wild-type was 97.68% (IQR 95.86%-97.92%) in the infection group higher than 92.6% (IQR 79.8%-97.9%) in the booster group (p=0.04). In conclusion, immunity against the wild-type virus at 3 months after two doses of CoronaVac-vaccinated HCWs with a history of COVID-19 infection was non-inferior to that of HCWs who received a booster dose of AZD1222. However, the infection group exhibited better immunity than the booster group at 6 months.