Antibody Responses 3-5 Months Post-Vaccination with mRNA-1273 or BNT163b2 in Nursing Home Residents

Abstract Nursing home residents often fail to mount robust responses to vaccinations and recent reports of breakthrough infections, particularly from variants of concern, raise questions about whether vaccination regimens elicit a sufficient humoral immune response or if booster doses are warranted. We examined SARS-CoV-2 antibody levels and neutralizing capacity in nursing home residents 3-5 months after 2 doses of mRNA-1273 or BNT163b2 vaccination as per recommended schedules. Nursing home residents were recruited from eight long-term care homes in Ontario, Canada, between March and July 2021. Antibody levels and neutralization capacity from a previously published convalescent cohort were used as a comparator. Serum SARS-CoV-2 IgA/G/M against spike (S) protein and its receptor-binding domain (RBD) were measured by validated ELISA, with assay cut-off at the mean and 3 standard deviations of a pre-COVID-19 population from the same geographic region. Antibody neutralization was measured against the wild-type strain of SARS-CoV-2 and the beta variant of concern (B.1.351). No neutralizing antibodies were detected in ∼20% of residents to the wild-type virus (30/155; 19%) or beta variant (27/134; 20%). Residents that received BNT163b2 had a ∼4-fold reduction in neutralization to the wild-type strain, and a ∼2-fold reduction in neutralization to the beta variant relative to those who received mRNA-1273. Current mRNA SARS-CoV-2 vaccine regimens may not have equivalent efficacy in nursing home residents. Our findings imply that differences in the humoral immune response may contribute to breakthrough infections, and suggest that consideration of the type of vaccine administered to older adults will have a positive impact on the generation of protective immunity.