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

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; 25: 588–597.