Immunogenicity after 6 months of BNT162b2 vaccination in frail or disabled nursing home residents: The COVID-A Study

Background There is incomplete information regarding evolution of antibody titers against SARS-CoV-2 after a two-dose strategy vaccination with BNT162b2 in older adults in long-term care facilities (LTCFs) with frailty, disability, or cognitive impairment. We aimed to determine IgG antibody titer loss in older adults in LTCFs. Methods This is a multicenter longitudinal cohort study including 127 residents (90 females and 37 males) with a mean age of 82.7 years (range 65-99) with different frailty and disability profiles in two LTCFs in Albacete, Spain. Residents received two doses of BNT162b2 as per label, and antibody levels were determined 1 and 6 months after the second dose. Age, sex, previous history of coronavirus disease 2019 (COVID-19), comorbidity (Charlson Index), performance in activities of daily living (Barthel Index), frailty (FRAIL instrument), and cognitive status were assessed. Results The mean antibody titers 1 and 6 months after the second vaccine dose were 32,145 AU/ml (SD 41,206) and 6182 AU/ml (SD 13,316), respectively. Across all participants, the median antibody titer loss measured 77.6% (interquartile range [IQR] 23.8%). Notably, the decline of titers in individuals with pre-vaccination COVID-19 infection was significantly lower than in those without a history of SARS-CoV-2 infection (72.2% vs. 85.3%; p < 0.001). The median titer decrease per follow-up day was 0.47% (IQR 0.14%) and only pre-vaccination COVID-19 was associated with lower rate of antibody decline at 6 months (hazard ratio 0.17; 95% confidence interval 0.07-0.41; p < 0.001). Frailty, disability, older age, cognitive impairment, or comorbidity were not associated with the extent of antibody loss. Conclusions Older adults in LTCFs experience a rapid loss of antibodies over the first 6 months after the second dose of BNT162b2 vaccine. Only pre-vaccination COVID-19 is associated with a slower rate of antibody decrease. Our data support immunization with a third dose in this vulnerable, high-risk population.