The Impact of Omicron Infection on Antibody Response and Attenuation: A Six-Month Follow-Up Study

Background Antibody patterns to ssevere acute respiratory syndrome coronavirus 2 (SARS-CoV-2) are the subject of current study, and the variations in antibodies to Omicron are yet unknown. The study investigated the six-month longitudinal dynamics and influencing factors of antibodies, including IgG, IgM, and neutralizing antibodies (NAbs), in healthcare workers (HCWs) following Omicron infection. Methods HCWs were recruited in Shanghai through multistage sampling, tested positive for SARS-CoV-2, and were followed up six times with blood sampling and questionnaires. The primary endpoints were the titers of the specific NAb against Omicron and the cut off index (COI) of IgG/IgM against Omicron. Antibody decay models were developed based on individual data of participants with single Omicron infection, and statistical analyses were conducted to explore influencing factors using Mann-Whitney U and Kruskal-Wallis tests. Results A total of 710 HCWs were enrolled, with IgG and NAb remaining high for five months but declining significantly in the sixth, but IgM declining rapidly throughout. After the single infection, IgG exhibited a mean short-term increase of 70.07 COI and a long-term elevation of 33.63 COI, with a gradual decline at a rate of − 0.0024 COI per day. IgM demonstrated a transient elevation, with a short-term boost of 23.66 COI and a modest long-term increase of 0.63, followed by a more rapid decay at − 0.0664 COI per day. NAb similarly rose significantly post-infection, with a short-term increase of 295.28 and a sustained long-term elevation of 292.07, declining at a rate of − 0.0021 COI per day. Reinfection occurred in 36.76% of HCWs, boosting antibody levels. Timing between infection and vaccination significantly influenced IgG/IgM waning but not NAbs. No associations were found between antibody decay and demographic or clinical factors. Conclusion While Omicron infection induces robust short-term antibody responses, immunity wanes significantly within six months, and reinfection temporarily boosts antibody levels. The findings highlight the limited durability of natural and hybrid immunity and underscore the need for timely booster vaccinations to sustain protection, particularly in high-risk groups like HCWs.