Post-infection and post-vaccination anti-COVID-19 antibody levels in relation to physical condition

To evaluate the antibody response against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) among residents of long-term care facilities (LTCFs) and to assess its relationship with their level of physical functioning. A prospective, multicenter study was conducted in eight LTCFs in southern Poland. Residents who provided informed consent completed a questionnaire addressing sociodemographic characteristics, comorbidities, vaccination status, and history of coronavirus disease 2019 (COVID-19). Physical functioning was assessed using the Barthel Index. Blood samples were collected to measure immunoglobulin G (IgG) antibodies against SARS-CoV-2 using enzyme-linked immunosorbent assay. Antibody levels were compared across groups defined by vaccination dose, prior infection, and degree of functional independence. A total of 429 residents participated (median age higher in the physically dependent group). Vaccination coverage was high (89%), predominantly with messenger RNA vaccines. Previous COVID-19 and receipt of booster doses were associated with higher antibody levels. Residents with moderate disability demonstrated the highest antibody titers, while those with very high or very low functional capacity showed lower levels. Antibody concentrations decreased with a longer interval since the last exposure to SARS-CoV-2 antigen (vaccination or infection). Residents of LTCFs develop a measurable humoral immune response to SARS-CoV-2 vaccination regardless of disability level. The association between functional status and antibody levels highlights the importance of individualized vaccination strategies in elderly populations.