Durability of antibody titers and associated factors after the booster dose of COVID-19 mRNA vaccination in Japanese SARS-CoV-2 infection-naive residents in geriatric intermediate care facilities.

Abstract

Aim: Elderly adults are at higher risk for severe COVID-19 infection. This multicenter, prospective cohort study assessed immunogenicity after COVID-19 vaccinations in elderly residents compared with staff in geriatric intermediate care facilities. Predictors of lower antibody titers were also examined.

Methods: Fifty-four residents and 117 staff who had received three doses of the COVID-19 mRNA vaccine between March 2021 and September 2022 were included. Anti-receptor binding domain antibody titers were measured 3-4 weeks and 6 months after the vaccinations. Adjusted geometric mean titers (GMT) were calculated using multivariable linear mixed effects models.

Results: After the first dose, residents had a significantly lower adjusted GMT than did staff (115 vs. 267 AU/mL, P < 0.01), whereas the adjusted GMT of residents was comparable to that of staff after the third dose (14 178 vs. 12 159 AU/mL, P = 0.63). However, 6 months later, the adjusted GMT of residents was less than half that of staff (1645 vs. 4302 AU/mL, P < 0.01). In residents, steroid users had a significantly lower adjusted GMT than did steroid nonusers.

Conclusions: The third dose of mRNA vaccine boosted the immune response of elderly residents. However, their antibody titers, particularly in steroid users, were highly attenuated 6 months after the last vaccination. For this population, attention should be focused on additional vaccinations. Geriatr Gerontol Int 2025; ••: ••-••.