The very high overall COVID-19 morbidity and mortality among nursing home (NH) residents led to their prioritization for early vaccination. In the US, most NH residents received BNT162b2 mRNA vaccination both because of its earlier Emergency Use Authorization approval and availability. NH residents that never had SARS-CoV-2 infection before the time of the vaccination series produced ∼¼ the antibody to this vaccine than that produced by healthy younger individuals.^1,2 With the rise of breakthrough infections in NH residents and others with immunocompromise, there is a significant need for characterization of the durability of immunity to inform public health policy. We report on 2-week and 6-month post-vaccination antibody levels from 120 NH residents (aged 48-100 years, median 76) and 91 ambulatory healthcare worker controls (aged 26-78 years, median 48) with and without SARS-CoV-2 infection prior to vaccination. We assessed anti-spike and anti-receptor binding domain (RBD) IgG, and serum neutralization titers, using a bead-based ELISA method and pseudovirus neutralization assay.¹ Anti-spike, anti-RBD and neutralization geometric mean levels dropped more than 84% over 6 months’ time in all groups (Fig. 1a-c) irrespective of prior SARS-CoV-2 infection. At 6 months post-vaccine, 70% of the infection-naive NH residents had neutralization titers at or below the lower limit of detection (LLD, 1:12 titer) compared to 16% at the LLD at 2 weeks after full vaccination (Supplemental Table 1). Controls and NH residents who survived prior infection had 19% and 35% respectively at LLD at 6 months post-vaccination. These data demonstrate significant 6-month antibody decline in all groups.

An improved understanding of the clinical consequences of this drop in humoral immunity is urgently needed to optimally inform boosting strategies and policy that are being actively considered in the recent CDC recommendation. However, in the absence of clinical evidence, extrapolating from laboratory values may be necessary. NH residents and healthcare workers were amongst the earliest populations vaccinated in the US and elsewhere, resulting in the longest time for immunity to wane. In particular, those infection-naive NH residents had lower initial post-vaccination humoral immunity immediately and exhibited the greatest declines 6 months later. Healthcare workers, given their younger age and relative good-health, achieved higher initial antibody levels and better maintained them, yet also experienced significant declines in humoral immunity. The rapid delta variant spread, vaccine breakthrough in NHs and community,^3-5 and rapid antibody decline support CDC’s recommended boosting NH residents to curb spread or prevent severe illness.