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The idea that tobacco smoking may protect against COVID-19 was always an improbable one. Both wreak terrible tolls on human lives; as of 13th July 2021, COVID-19 has killed an estimated 4 million people while tobacco smoking kills 8 million people every year.1 2 Yet some early evidence appeared to indicate that smoking tobacco was linked to a reduced risk of COVID-19 infection and death. This finding unsurprisingly generated substantial interest among researchers, the medical profession and the public.3
The paper by Clift et al 4 in this issue advances our understanding of the links between tobacco smoking and COVID-19 by combining a range of relevant data to employ two separate analytic approaches. Together, these analyses suggest a causal role for tobacco smoking in COVID-19 severity. The authors linked data from UK Biobank with primary care records, COVID-19 testing data, hospital admissions and death certificates to perform both observational and Mendelian randomisation analyses. COVID-19 testing data were available only up until August 2020, meaning that data on confirmed infections were concentrated in hospital settings. The observational analyses did not find that current smokers were more likely to have confirmed COVID-19 infection, but they were more likely to be admitted to hospital and to die from the disease. For example, in models adjusting for age and sex, current smokers were more likely than never smokers to be admitted to hospital …
Contributors AAL wrote the first draft. CM revised this for intellectual content and interpretation of relevant data. Both authors approved the final version for submission and are joint guarantors.
Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors. AAL and CM are grateful for support from the NIHR School for Public Health Research.
Competing interests None declared.
Provenance and peer review Commissioned; externally peer reviewed.