Background This study aimed to examine associations between smoking and COVID-19 relevant outcomes, taking into account the influence of inequalities and adjusting for potential confounding variables.

Methods Cross-sectional data were used from an online study of adults in the UK (n=53 002). Main outcome measures were confirmed and suspected COVID-19, worry about catching or becoming seriously ill from COVID-19 and adherence to protective behaviours. Covariates included age, sex, ethnicity, education (post-16 qualifications: yes/no), key worker status and comorbid health conditions.

Results Compared with never smokers (0.26% (95% CI 0.21% to 0.33%)), prevalence of confirmed COVID-19 was higher among current (0.56% (0.41% to 0.75%)) but not ex-smokers (0.19% (0.13% to 0.28%)). Associations were similar before (current: OR=2.14 (1.49–3.08); ex-smokers: OR=0.73 (0.47–1.14)) and after (current: OR=1.79 (1.22–2.62); ex-smokers: OR=0.85 (0.54–1.33)) adjustment. For current smokers, this was moderated by socio-economic position, with higher rates only seen in those without post-16 qualifications (OR=3.53 (2.04–6.10)). After including suspected cases, prevalence was higher among current smokers (11.2% (10.6% to 11.9%), OR=1.11 (1.03–1.20)) and ex-smokers (10.9% (10.4% to 11.5%), OR=1.07 (1.01–1.15)) than never smokers (10.2% (9.9% to 10.6%)), but remained higher only among ex-smokers after adjustment (OR=1.21 (1.13–1.29)). Current and ex-smokers had higher odds than never smokers of reporting significant stress about becoming seriously ill from COVID-19 (current: OR=1.34 (1.27–1.43); ex-smokers: OR=1.22 (1.16–1.28)). Adherence to recommendations to prevent spread of COVID-19 was high (96.3% (96.1% to 96.4%)), but lower among current than never smokers (OR=0.70 (0.62–0.78)).

Conclusions In a population sample, current smoking was independently associated with self-reported confirmed COVID-19 infection. There were socio-economic disparities, with the association only apparent among those without post-16 qualifications. Smokers reported lower adherence to guidelines despite being more worried than non-smokers about catching or becoming seriously ill from COVID-19.