Age- and sex-based changes in spike protein antibody status after SARS-CoV-2 vaccination and effect of past-infection in healthcare workers in Osaka

Objective We aimed to compare the changes in SARS-CoV-2 spike protein antibody titres based on age group and sex using paired blood sampling after vaccination in association with the presence of nucleocapsid protein antibody. Methods All participants were healthcare workers at Yao Municipal Hospital in Osaka who voluntarily provided peripheral blood samples (n = 636, men/women 151/485, mean age 45 years). We investigated the serial changes in SARS-CoV-2 spike protein antibody titres at 1 and 7 months after the second vaccination regarding their relationship with sex and age group. At 7 months, we also examined anti-nucleocapsid assays. Antibody titres were shown as logarithmic values and the differences were assessed using a paired or unpaired student’s t-test as appropriate. Results Among participants younger than 30 years, the antibody titres of spike protein were significantly higher in women one (p = 0.005) and seven (p = 0.038) months after vaccination. However, among those aged 30–49 years, the antibody titres were not different between the sexes at either follow-up time point. In contrast, among those aged 50–59 years, between-sex differences in antibody titres were observed only at 7 months, which was associated with a significant reduction in men. A significant negative correlation was observed between the antibody titres for spike protein at both time points in participants with positive nucleocapsid protein antibody at 7 months (r = − 0.467, p = 0.043), although a significant positive correlation was observed in those with negative results (r = 0.645, p Conclusions Between-sex differences in SARS-CoV-2 spike protein antibody titres by paired blood sampling at different time points after vaccination depended on age group. The presence of nucleocapsid protein antibody was associated with changes in spike protein antibody titres after vaccination.