Influencing factors of antibody response after 2 doses of inactivated COVID-19 vaccine among adults aged ≥18 years in Chongqing, China: A cross-sectional serological study

The study aimed to explore the influencing factors after 2 doses of inactivated COVID-19 vaccines (Sinopharm/BBIBP-CorV) in the real world. We conducted a cross-sectional serological study involving 316 volunteers aged ≧ 18 years from 7 vaccination hospitals in the Yubei districts, Yuzhong districts, and Jiulongpo districts of Chongqing. Serum samples were obtained about 1 month after 2 dose vaccination, and Nabs were tested using the pseudovirus-based neutralizing assay. Chi-square or Fisher exact tests were used to analyze the seropositive rates, while the Kruskal-Wallis H or Mann-Whitney U tests were used to analyze differences in Nabs level among stratified groups. Logistic regression analyses were conducted to identify the influencing factors. The results showed that seropositive rates was 76.27% and the GMT was 26.13 (95% CI: 23.03-29.66) after 2 doses of COVID-19 inactivated vaccination. The risk of being seropositive in 18 to 29, 30 to 39, 40 to 49, 50 to 59, and 60 to 69 years were 12.808-fold, 8.041-fold, 7.818-fold, 6.275-fold, 1.429-fold compared with the people aged ≥ 70 years (P < .05), and the risk of being seropositive of intervals 15 to 21 and 22 to 28 days were 0.273-fold and 0.286-fold compared with >28 days (P < .05), respectively. In conclusion, age may be a risk factor for reduced antibody production, and longer vaccination intervals-may be a protective factor that increases antibody production. These findings contribute to informing future vaccination strategies.