Resident Factors Associated With Breakthrough SARS-CoV-2 Infections

OBJECTIVE: To examine incidence of and resident characteristics associated with breakthrough infections (BTIs) and severe illness among residents with 2 messenger RNA (mRNA) vaccinations. DESIGN: Retrospective cohort study. SETTING AND PARTICIPANTS: Nursing home (NH) residents who completed their primary series of mRNA COVID-19 vaccination by March 31, 2021. METHODS: Electronic health records and Minimum Data Set assessments from a multistate NH data consortium were used to identify BTI and severe illness (a composite measure of hospitalization and/or death within 30 days of BTI) occurring prior to November 24, 2021. A t test for differences in means was used to compare covariates for residents with and without BTI. Finally, we estimated incidence rate ratios (IRRs) for BTI with 95% CIs using a modified Poisson regression approach, comparing residents with BTI vs residents without. We adjusted for facility fixed effects in our model. RESULTS: Our sample included 23,172 residents from 984 NHs who were at least 14 days past their second mRNA vaccine dose. Of those, 1173 (5%) developed an incident COVID-19 BTI (mean follow-up time: 250 days). Among residents with BTI, 8.6% were hospitalized or died within 30 days of BTI diagnosis. Factors associated with severe illness included age ≥85 years (IRR 2.08, 95% CI 1.08-4.02, reference age <65 years), bowel incontinence (IRR 1.73, 95% CI 1.01-2.99), coronary artery disease (IRR 1.96, 95% CI 1.31-2.94), chronic kidney disease (IRR 1.65, 95% CI 1.07-2.54), and schizophrenia (IRR 2.38, 95% CI 1.19-4.75). CONCLUSIONS AND IMPLICATIONS: Among vaccinated NH residents, BTIs and associated severe illness are rare. Residents aged ≥85 years and with certain comorbidities appear to be the most vulnerable. Given that the pandemic continues and testing policies have relaxed, these data provide prognostic information for NH facilities faced with continued outbreaks.