Effectiveness of a Fourth Dose of COVID-19 mRNA Vaccine in Older Long-Term Care Residents: More Evidence

Residents of long-term care facilities are at high risk for severe COVID-19. In the Omicron era, would a fourth dose of mRNA vaccine (mRNA-1273 or BNT162b2) benefit this population? A Canadian test-negative cohort study between December 2021 and April 2022 involving >61,000 long-term care residents (aged >60 years, 9.4% immunocompromised) provides an answer.

Compared with vaccine effectiveness in residents who had received their third dose ≥84 days before being tested, effectiveness of a fourth dose was 19% (any infection), 31% (symptomatic infection), and 40% (severe outcomes [hospital admission or death]). Effectiveness of the third dose waned with time (i.e., ≥84 days before testing vs. more recently). For residents receiving at least one dose compared with those who were unvaccinated, effectiveness increased with each dose: 37% (any infection), 55% (symptomatic infection), and 77% (severe outcomes) for three doses, and 49%, 69%, and 86% for four doses. Heterologous vaccine dosing had little impact on effectiveness.