Initially High Correlation between Air Pollution and COVID-19 Mortality Declined to Zero as the Pandemic Progressed: There Is No Evidence for a Causal Link between Air Pollution and COVID-19 Vulnerability

Wu et al. found a strong positive association between cumulative daily county-level COVID-19 mortality and long-term average PM2. 5 concentrations for data up until September 2020. We replicated the results of Wu et al. and extended the analysis up until May 2022. The association between PM2. 5 concentration and cumulative COVID-19 mortality fell sharply after September 2020. Using the data available from Wu et al. ’s “updateddata” branch up until May 2022, we found that the effect of a 1 μg/m3 increase in PM2. 5 was associated with only a +0. 603% mortality difference. The 95% CI of this difference was between −0. 560% and +1. 78%, narrow bounds that include zero, with the upper bound far below the Wu et al. estimate. Short-term trends in the initial spread of COVID-19, not a long-term epidemiologic association, caused an early correlation between air pollution and COVID-19 mortality.