Current Smoking and Risk of Coronavirus Infection and Illness in a Highly Controlled Challenge Study: A Re-analysis of the British Cold Study

INTRODUCTION: Meta-analyses have shown an association between smoking and the risk of Coronavirus Disease 2019 (COVID-19) disease severity, but the risk of smoking and coronavirus infection is less clear. AIMS AND METHODS: We re-analyzed data from the British Cold Study, a 1986–1989 challenge study that exposed 399 healthy adults to 1 of 5 “common cold” viruses (including n = 55 for coronavirus 229E). Participants with cotinine levels below 15 ng/mL (noncurrent smokers) were compared with participants with higher cotinine levels or self-reported smoking (current smokers). We calculated overall and coronavirus-specific unadjusted and adjusted relative risks (RRs) for current smoking and each outcome (infection and illness), and tested whether each association was modified by the type of respiratory virus. RESULTS: Current smokers had a higher adjusted risk than noncurrent smokers for infection (adjusted RR [aRR] = 1.12, 95% CI: 1.01, 1.25) and illness (aRR = 1.48, 95% CI: 1.11, 1.96). Neither association was modified by an interaction term for smoking and type of virus (infection: p = .44, illness: p = .70). The adjusted RR estimates specific to coronavirus 229E for infection (aRR = 1.22, 95% CI: .91, 1.63) and illness (RR = 1.14, 95% CI: .62, 2.08) were not statistically significant. CONCLUSIONS: These RRs provide estimates of the strength of associations between current smoking and infection and illness that can be used to guide tobacco control decisions. IMPLICATIONS: Systematic reviews and meta-analyses have found an association between smoking and COVID-19 disease severity, but fewer studies have examined infection and illness. The British Cold Study, a high-quality challenge study that exposed healthy volunteers to respiratory viruses including a coronavirus, provides an opportunity to estimate the RR for current smoking and infection and illness from coronaviruses and other viruses to guide tobacco control decisions. Compared with noncurrent smokers, current smokers had a 12% increased risk of having a laboratory-confirmed infection and a 48% increased risk of a diagnosed illness, which was not modified by the type of respiratory virus including a coronavirus.