Abstract
Despite the high efficacy of the BNT162b2 vaccine in the general population, data on its immunogenicity among frail elderly individuals are limited. Recently, levels of anti-SARS-CoV-2 spike IgG antibodies and serum neutralization titers were confirmed as good immune markers of protection against the virus, with evidence showing a reverse correlation between these two parameters and susceptibility to infection. Here we analyzed sera from 138 nursing home residents (median age of 88.9 years) and 312 nursing home staff (median age of 50.7 years) to determine the humoral response to two doses of the BNT162b2 vaccine, and found markedly decreased serum anti-spike antibody levels and neutralization titers in the nursing home resident (NHR) group, with over 11% non-responders compared to only 1.3% among the controls. Moreover, three months post-vaccination, a significant decrease in antibody titers was observed in COVID-19-naive nursing home residents. Subsequent flow cytometry and interferon gamma secretion analyses indicated that antibody non-responders among NHRs also failed to mount cellular responses. The presented data emphasize that additional measures are needed in the population of frail elderly individuals. Given the high proportion of non-responders among NHRs, continued monitoring should be considered in this group.
Highlights
The COVID-19 pandemic has disproportionately affected the elderly and frail populations, who accounted for the majority of deaths [1]
Anti-spike IgG antibody levels and their neutralization potential have been correlated with vaccine efficacy in preventing breakthrough infections [11], and in the context of variants of concern, like the B.1.617.2 strain designated as Delta [12] and—to a much lesser degree—Omicron [13]
nursing home resident (NHR) presented a relatively broad range of post-vaccination antibody titers, while the spread was smaller in the control group
Summary
The COVID-19 pandemic has disproportionately affected the elderly and frail populations, who accounted for the majority of deaths [1]. Real-world data demonstrating post-vaccination antibody responses in the groups most susceptible to SARS-CoV-2-related morbidity and mortality remain limited. Observations from the few available studies in nursing home residents show conflicting results, with some reporting very good immunogenicity following the administration of two doses [7,8] and others indicating decreased levels of seroconversion and neutralization [9,10]. Reports on vaccine efficacy in the most vulnerable groups indicated that breakthrough infections occur in a small percentage of vaccine recipients, with nursing home residents becoming disproportionally more affected than the staff [14]. Given the vulnerability of this group, we decided to conduct a study comparing the post-vaccination antibody response in NHRs to the working-age population of NHS two weeks post-vaccination. Samples were obtained from a subset of the NHRs and additional assays were performed to assess the cellular response against SARS-CoV-2
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