Review Meta Analysis
Influenza immunisation may be associated with reduced risk of COVID infection (RR 95% CI 0.76-0.90).pearl
- Wanying Su, Hao Wang, Chenyu Sun, Ning Li, Xianwei Guo, Qiuxia Song, Qiwei Liang, Mingming Liang, Xiuxiu Ding, and Yehuan Sun.
- Department of Epidemiology and Health Statistics, School of Public Health, Anhui Medical University, Anhui, P. R. China.
- Am J Prev Med. 2022 Jul 1; 63 (1): 121-130.
IntroductionThe association between influenza vaccination and COVID-19 remains controversial. This meta-analysis aimed to investigate whether influenza vaccination reduces the susceptibility and severity of SARS-CoV-2 infection.MethodsA systematic literature search of PubMed, Web of Science, the Cochrane Library, Embase, China National Knowledge Infrastructure, SinoMed, Wanfang Data Knowledge Service Platform, and China Science and Technology Journal VIP Database was conducted from database inception to August 2021. The pooled RR with 95% CI was used to estimate the effect of influenza vaccination on COVID-19. The I2 value was used to assess heterogeneity. If I2>50%, the random-effects model was used as the pooling method.ResultsA total of 23 published articles with 1,037,445 participants were identified. This meta-analysis showed that influenza vaccination was associated with reduced risk of COVID-19 infection (RR=0.83, 95% CI=0.76, 0.90) and hospitalization (RR=0.71, 95% CI=0.59, 0.84), although not significantly associated with intensive care unit admission and death (risk of intensive care unit admission: RR=0.93, 95% CI=0.64, 1.36; risk of death: RR=0.83, 95% CI=0.68, 1.01). Further analysis suggested that the tetravalent influenza vaccine may be associated with a reduced risk of COVID-19 infection (RR=0.74, 95% CI=0.65, 0.84).DiscussionThe results suggest that influenza vaccination is associated with reduced susceptibility to or disease severity of COVID-19 and that influenza vaccination may reduce the risk of COVID-19 and improve clinical outcomes.Copyright © 2022 American Journal of Preventive Medicine. Published by Elsevier Inc. All rights reserved.
The usual 'correlation is not causation' qualifier is very necessary here. Perhaps doubly-so because this is a meta-analysis using pooled data of over 1 million people.
It's completely possible that someone who chooses to receive an influenza vaccine is also someone who makes more cautious health decisions and is more risk-averse, reducing their COVID exposure risk. The vaccinated are also more likely to be from better health-serviced locations and probably from higher socio-economic groups.
Still, interesting association nonetheless.
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