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Effectiveness of a Second COVID-19 Vaccine Booster on All-Cause Mortality in Long-Term Care Facility Residents and in the Oldest Old: A Nationwide, Retrospective Cohort Study in Sweden
22 Pages Posted: 12 May 2022More...
Background: The effect of a second booster dose of COVID-19 vaccine on the risk of death from all causes among the oldest and frailest individuals is unknown. We aimed to investigate the relative vaccine effectiveness of a second booster dose against all-cause mortality in residents of long-term care facilities and in the oldest old.
Methods: Two nationwide matched cohorts were formed using Swedish nationwide registers. In the first, residents of LTCFs who were given a second booster with either BNT162b2 or mRNA-1273 from 1 January 2022 onwards were matched 1:1 exactly on birth year and county of residence to residents given only the first booster (N=25,252). In the second, all individuals living in Sweden aged >80 years who were given the second booster were matched 1:1 to individuals given the first booster (N=397,394). Baseline in each matched pair was the date of vaccination in second-booster recipients. The outcome was all-cause mortality until 29 March 2022.
Findings: From 7 days after baseline and onwards, there were 330 deaths in the LTCF cohort during a median follow-up of 21 days. Compared to the first booster, the second booster had an adjusted relative vaccine effectiveness of 31% (95% CI, 14-45). In the cohort of all individuals aged >80 years, there were 1025 deaths during a median follow-up of 20 days. The adjusted relative vaccine effectiveness of the second booster in this cohort was 42% (95% CI, 35-49), with greater effectiveness (P=0·004 for interaction) when compared to first-booster recipients in which more than 4 months had passed since vaccination (52%, 95% CI, 42-61).
Interpretation: As compared with a first booster, a second booster dose with either BNT162b2 or mRNA-1273 was associated with reduced short-term risk of death from all causes among residents in LTCFs and in the oldest old during the Omicron era. These findings suggest that promoting a high uptake of booster doses in old and frail people may prevent premature deaths.
Funding: There was no funding source for this study.
Declaration of Interest: We declare no competing interests.
Ethical Approval: The study was approved by the Swedish Ethical Review Authority (no. 2021-00094) who waived the informed consent requirement given the retrospective design
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