Mediating effect of smoking on the relationship between educational status and hospitalization in China with COVID-19: a cross-sectional study

Abstract Background: Educational disparities in COVID-19 outcomes are well documented in Western countries, but evidence from China is limited. This study explored the role of smoking in these disparities. Methods: We conducted a cross-sectional study in China between January 28 and February 21, 2023. Participants who reported positive SARS-CoV-2 results via RT‒PCR and/or IgM‒IgG antigen tests provided self-reported data on COVID‒19 hospitalization, educational status, and smoking status through an online questionnaire. Logistic regressions with and without inverse probability weighting estimated odds ratios (ORs) for COVID-19 hospitalization by educational status, adjusting for potential confounders. The Karon‒Holm‒Breen (KHB) method was used to estimate the proportion of mediation attributable to smoking status. Results: Of the 25,827 participants (56.4% male; mean age 40.9 years), 1652 (6.83%) were hospitalized, and higher ORs for COVID-19 hospitalization were found in those with primary school education or below (OR: 1.84), junior high school (OR: 1.48), high school/technical secondary school (OR: 1.44), and smoking history (OR: 1.52). Smoking mediated the relationship between educational status and hospitalization, with mediation proportion ranging from 7.62% to 13.34%, varying by sex. Conclusion: This study highlights an educational gradient in COVID-19 hospitalization in China, with smoking as a partial mediator.