Antibody response after SARS-CoV-2 infection or vaccination in China: A cross-sectional study

It is crucial to understand how antibodies are generated after the individual has been infected or vaccinated to control the COVID-19 pandemic and develop future vaccination strategies. The level of SARS-CoV-2 IgG/IgM was assessed in 348 plasma samples in the current study. Results showed that the SARS-CoV-2 IgG level of mild/moderate infections was higher than that of asymptomatic infections. Strong correlations were found between the SARS-CoV-2 IgG and the geometric mean neutralizing titers (GMTs), detected using pseudotyped neutralization assay, against BA.4/5 ( r = 0.776, p < 0.001) or XBB.1.5 ( r = 0.329, p = 0.004), while SARS-CoV-2 IgM showed a weaker correlation with BA.4/5 ( r = 0.247, p = 0.030). The GMTs against BA.4/5 were higher in mild/moderate infections than in asymptomatic infections. Moreover, we found that the convalescent patients with vaccination had higher antibody responses than the convalescent patients without vaccination. The XBB.1.5 variant, however, was able to escape the immune response induced by BA.5 breakthrough infection and vaccination. To ensure the population maintains a sufficient level of protective antibodies, it might be required to periodically enhance immune responses by administering antigens obtained from the circulating variants. It is highly essential to optimize vaccination protocols in practice settings and develop future vaccines that offer a broader spectrum of protection. • SARS-CoV-2 IgG levels could reflect neutralization ability to a certain extent. • XBB.1.5 variant escaped the immune response induced by BA.5. • The convalescent patients with vaccination had a high antibody response.