OBJECTIVE To explore the risk factors for serum COVID-19 antibodies in the population of Fuzhou to provide scientific basis for prevention and control strategies.

METHODS The prospective study and the multi-stage stratified random sampling method were performed to select at least 200 subjects from each of the 12 counties (cities) in Fuzhou. Questionnaires follow-ups and serum collections were conducted in Mar, Jun, Sep, and Dec. 2024, respectively. The antibody levels in Dec. were divided into a high protective antibody group (IgG antibody ≥ 50 AU/ml) and a low protective antibody group (IgG antibody ≤ 20 AU/ml). The influencing factors of serum antibody levels were analyzed by multivariate logistic regression model.

RESULTS A total of 2816 subjects were enrolled. In Mar, 1454 subjects with high-protective antibodies were identified. After nine months of follow-up, of the 1454 subjects, 344 had high protective antibodies and 369 had low protective antibodies in Dec.. There were statistically significant differences in age, presence of typical symptoms after infection, underlying diseases, surgical history, healing time, smoking and drinking histories between the high and low antibody groups (P < 0.05). Multivariate logistic regression model showed that older age, underlying diseases, history of surgery, smoking and drinking were risk factors which could reduce antibody levels (P < 0.05), while typical symptoms after infection and longer recovery time were protective factors which could increase antibody levels (P < 0.05). After the COVID-19 infection in spring of 2024, the serum antibody levels in Fuzhou residents showed the downward trend, especially after Sep. 2024, with a more pronounced downward trend.

CONCLUSIONS According to the risk factors of COVID-19 antibody levels, prevention and control efforts should be focused on the key population. It is necessary to strengthen health education and carry out vaccination to maintain the levels of immunity to protect population from COVID-19 infection.