Long-term effects of extreme smoke exposure on COVID-19: A cohort study

In early 2014, the Hazelwood coalmine fire covered the regional Australian town of Morwell in smoke and ash for 45 days. One of the fire’s by-products, PM2.5, has been linked higher rates of COVID-19 infection to increased expression of the ACE2 receptor, which the COVID-19 virus uses to infect cells throughout the body. However, it is unclear whether the effect persists for years after exposure. In this study, we surveyed a cohort established prior to the pandemic to determine whether PM2.5from the coalmine fire increased long-term vulnerability to COVID-19 infection and severe disease.In late 2022, 612 members of the Hazelwood Health Study’s adult cohort, established in 2016/17, participated in a follow-up survey including standardised items to capture COVID-19 infections, hospitalisations, and vaccinations. Associations were evaluated in crude and adjusted logistic regression models, applying statistical weighting for survey response and multiple imputation to account for missing data, with sensitivity analyses to test the robustness of results.A total of 271 (44%) participants self-reported or met symptom criteria for at least one COVID-19 infection. All models found a positive association, with odds of infection increasing by between 4-21% for every standard deviation (12.3µg/m3) increase in mine fire-related PM2.5exposure. However, this was not statistically significant in any model. There were insufficient hospitalisations to examine severity (n=7; 1%).The findings were inconclusive in ruling out an effect of PM2.5exposure from coalmine fire on long-term vulnerability to COVID-19 infection. Given the positive association that was robust to modelling variations as well as evidence for a causal mechanism, it would be prudent to treat PM2.5from fire events as a risk factor for long-term COVID-19 vulnerability until more evidence accumulates.