Duration of vaccine effectiveness against SARS-CoV2 infection, hospitalisation, and death in residents and staff of Long-Term Care Facilities (VIVALDI): a prospective cohort study, England, Dec 2020-Dec 2021

Abstract

Background Long-term care facilities (LTCF) have been prioritised for vaccination, but data on potential waning of vaccine effectiveness (VE) and the impact of booster doses in this vulnerable population remains scarce. Methods We included residents and staff from 331 LTCFs enrolled in VIVALDI (ISRCTN 14447421), who underwent routine PCR testing between Dec 8, 2020 - Dec 11, 2021 in a Cox proportional hazards regression, estimating VE against SARS-CoV2 infection, COVID-19-related hospitalisation, and COVID-19-related death after 1-3 vaccine doses, stratifying by previous SARS-CoV2 exposure. Results For 15,518 older residents, VE declined from 50.7% (15.5, 71.3) to 17.2% (-23.9, 44.6) against infection; from 85.4% (60.7, 94.6) to 54.3% (26.2, 71.7) against hospitalisation; and from 94.4% (76.4, 98.7) to 62.8% (32.9, 79.4) against death, when comparing 2-12 weeks and ≥12 weeks after two doses. For 19,515 staff, VE against infection declined slightly from 50.3% (32.7, 63.3) to 42.1% 29.5, 52.4). High VE was restored following a third dose, with VE of 71.6% (53.5, 82.7) and 78.3% (70.1, 84.3) against infection and 89.9% (80.0, 94.6) and 95.8% (50.4, 99.6) against hospitalisation, for residents and staff respectively; and 97.5% (88.1, 99.5) against death for residents. Interpretation Substantial waning of VE is observed against all outcomes in residents from 12 weeks after a primary course of AstraZeneca or mRNA vaccines. Boosters restore protection, and maximise immunity across all outcomes. These findings demonstrate the importance of boosting and the need for ongoing surveillance of VE in this vulnerable cohort. Funding UK Government Department of Health and Social Care.