Association between long-term smoking cessation and COVID-19 outcomes: Findings from a nationwide cross-sectional online survey in China

INTRODUCTION: Smoking has been identified as a potential risk factor for adverse COVID-19 outcomes. This study aimed to investigate the association between long-term smoking cessation and COVID-19 outcomes. METHODS: In this nationwide, cross-sectional online survey conducted in China (January-February 2023), 22709 adults with COVID-19, confirmed by nucleic acid amplification test (NAAT) or SARS-CoV-2 antigen testing, were included. Smoking status was self-reported and classified as never smokers, long-term ex-smokers (≥10 years), ex-smokers (<10 years), and current smokers. COVID-19 outcomes, including pneumonia, hospitalization, and severe COVID-19, were compared across these groups. Logistic regression models were used to adjust for potential confounders. Sensitivity analyses included all self-reported cases irrespective of test confirmation. RESULTS: Among 22709 COVID-19-positive participants, current smokers and ex-smokers <10 years exhibited significantly higher proportion of pneumonia, hospitalization, and severe COVID-19 than never smokers. Current smokers (AOR=3.18; 95% CI: 2.90-3.48) and ex-smokers quit <10 years (AOR=3.48; 95% CI: 2.96-4.09) had increased odds of pneumonia, whereas long-term ex-smokers showed no elevated risk (AOR=1.12; 95% CI: 0.45-2.41). These associations were consistent in sensitivity analyses. Other factors significantly associated with pneumonia included sex, education level, residence, obesity, income, and chronic conditions. CONCLUSIONS: Long-term smoking cessation was not associated with an elevated risk of COVID-19-related pneumonia compared to never smokers, whereas ex-smokers (<10 years) and current smokers remained high-risk groups. These findings support the potential benefits of sustained cessation, although further longitudinal studies are needed to confirm and extend these findings.