Abstract
To investigate the humoral immunity and clinical characteristics of Chinese college students after experiencing a BA.5/BF.7 and/or XBB.1.5 wave. We enrolled 876 college students who received 2-3 vaccination doses of COVID-19 and followed by BA.5/BF.7 and/or XBB.1.5 breakthrough infections between January 2022 and October 2023. IgG and total antibodies against SARS-CoV-2 were measured by chemiluminescent immunoassay. Neutralizing antibodies were detected using a pseudovirus neutralization assay. Meanwhile, we created an Enterprise WeChat link for college students to self-report SARS-CoV-2 infections and clinical symptoms of COVID-19. We observed that among college students, the most common symptoms upon SARS-CoV-2 infection were fever, fatigue, and sore throat. Moreover, reinfected college students had higher levels of total antibodies and neutralizing antibodies against BA.5, XBB.1.5 and EG.5.1, especially after experiencing the XBB.1.5 wave. Finally, the neutralizing effect against the newly emerged Omicron subvariants XBB.1.5 and EG.5.1 is limited among the college students. Our study demonstrates that hybrid immunity, built from breakthrough infections and reinfections, enhances total antibody levels and bolsters neutralizing activity, contributing to milder clinical presentations upon reinfection. However, neutralization efficacy against newer subvariants, such as XBB.1.5 and EG.5.1, remains compromised.