Abstract
BACKGROUND: The impact of e-cigarettes on COVID-19 remains unclear. This study aims to assess the relationship between e-cigarette use and COVID-19 diagnosis and other related outcomes. METHODS: This systematic review and meta-analysis searched studies from 2019 to April 2nd, 2024, in Medline (via OVID), EMBASE, Scopus and the Cochrane Central Register of Controlled Trials for eligible observational studies. RESULTS: Among the initially identified 1116 items, a total of 20 studies met the inclusion criteria. The meta-analysis revealed that e-cigarette use was significantly associated with higher odds of COVID-19 diagnosis (N = 14, adjusted odds ratio, OR 1.25, 95% confidence interval, CI 1.07 to 1.47, I2 = 62%). This association was more pronounced among the youth (N = 4, adjusted OR 1.78, 95% CI 1.17 to 2.72, I2 = 75%) and current e-cigarette users (N = 14, adjusted OR 1.30, 95% CI 1.10 to 1.55, I2 = 55%). Though the association was not significant among cohort or case-control studies at first, the robust results were shown excluding low-quality studies (N = 3, adjusted OR 1.25, 95% CI 1.03 to 1.50, I2 = 0%). The results remained consistent in leave-one-out analyses. Drawing from the available but limited research, no significance was observed between e-cigarette use or other COVID-19 outcomes including severe COVID-19, COVID-19-related death, symptoms or hospital admission. Heterogeneity and risk of bias should be noticed when explaining our results. CONCLUSIONS: E-cigarette use was associated with an increased risk of COVID-19 diagnosis, particularly among youth and current users. Further high-quality evidence is needed to assess the overall health effects of e-cigarettes, with a particular focus on the youth and current users.