Real-world Effectiveness of mRNA COVID-19 Vaccines Among US Nursing Home Residents Aged ≥65 Years in the Pre-Delta and High Delta Periods
Yun Lu, Arnstein Lindaas, Kathryn Matuska, Héctor S. Izurieta, Rowan McEvoy, Mikhail Menis, Xiangyu Shi, Whitney R. Steele, Michael Wernecke, Yoganand Chillarige, Hui Lee Wong, Jeffrey A. Kelman, Richard A. Forshee
Abstract
Background: Long-term care residents were among the most vulnerable during the COVID-19 pandemic. We estimated vaccine effectiveness of mRNA COVID-19 vaccines in Medicare nursing home residents aged ≥65 years during pre-Delta and high Delta periods. Methods: We conducted a retrospective cohort study from 13 December 2020 to 20 November 2021 using Medicare claims data. Exposures included 2 and 3 doses of Pfizer-BioNTech and Moderna COVID-19 vaccines. We used inverse probability weighting and Cox proportional hazards models to estimate absolute and relative vaccine effectiveness. Results: Two-dose vaccine effectiveness against COVID-19-related death was 69.8% (95% CI, 65.9%‒73.3%) during the pre-Delta period and 55.7% (49.5%‒61.1%) during the high Delta period, without adjusting for time since vaccination. We observed substantial waning of effectiveness from 65.1% (54.2%‒73.5%) within 6 months from second-dose vaccination to 45.2% (30.6%‒56.7%) ≥6 months after second-dose vaccination in the high Delta period. Three doses provided 88.7% (73.5%‒95.2%) vaccine effectiveness against death, and the incremental benefit of 3 vs 2 doses was 74.6% (40.4%‒89.2%) during high Delta. Among beneficiaries with a prior COVID-19 infection, 3-dose vaccine effectiveness for preventing death was 78.6% (50.0%‒90.8%), and the additional protection of 3 vs 2 doses was 70.0% (30.1%‒87.1%) during high Delta. Vaccine effectiveness estimates against less severe outcomes (eg, infection) were lower. Conclusions: This nationwide real-world study demonstrated that mRNA COVID-19 vaccines provided substantial protection against COVID-19-related death. Two-dose protection waned after 6 months. Third doses during the high Delta period provided significant additional protection for individuals with or without a prior COVID-19 infection.