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 one and seven months after the second vaccination regarding their relationship with sex and age group. At seven months, we also examined anti-nucleocapsid assays.
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 to 49 years, the antibody titres were not different between the sexes at either follow-up time point. In contrast, among those aged 50 to 59 years, between-sex differences in antibody titres were observed only at seven months, which was associated with a significant reduction in men. A significant positive correlation was observed between the antibody titres for spike protein at both time points (r = 0.645, p < 0.001), although a significant negative correlation was observed in participants with positive nucleocapsid protein antibody at seven months (r=-0.467, p = 0.043).
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.