The COVID-19 pandemic, caused by SARS-CoV-2, profoundly impacted global health systems and economies. Vaccination and diagnostic advancements were pivotal in managing the pandemic. This systematic review evaluates antibody levels in adults following complete COVID-19 vaccination and examines the prevalence of infections in vaccinated populations. A systematic review adhering to PRISMA guidelines was conducted, focusing on studies analyzing antibody levels at least 14 days after full vaccination with FDA- or EMA-approved vaccines. Five European studies meeting the inclusion criteria were selected. Data were extracted and synthesized from studies involving 6280 participants aged 19 to 105, with an average of 11% having prior exposure to SARS-CoV-2. Antibody levels were analyzed over time, and the incidence of post-vaccination COVID-19 cases was recorded. The reviewed studies demonstrated that antibody levels peaked shortly after vaccination but gradually declined over time. Individuals with prior SARS-CoV-2 infection exhibited higher antibody titers than those without prior exposure. After the first dose, the Pfizer–BioNTech vaccine led to significantly higher antibody levels than the Oxford–AstraZeneca vaccine, especially in those without prior infection. Across all studies, the incidence of COVID-19 among vaccinated individuals was low (0.1–3.8% for 144–302 days post-vaccination). Vaccination reduced severe outcomes despite decreasing antibody levels. The decline in new COVID-19 cases and related deaths is attributed to widespread vaccination, natural immunity, and virus mutations reducing severity. Further studies are warranted to explore antibody persistence and optimal vaccination strategies.

Aim 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. Subject and methods 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. Results 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). Conclusion 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.