Temporal association between ambient PM2.5 and COVID-19 incidence in Abidjan, Côte d’Ivoire, during the first year of the pandemic (March 2020 – March 2021)

This study, conducted within the IAQWA (Improving Air Quality in West Africa) project funded by the European Make Our Planet Great Again (MOPGA) program, investigates the temporal association between ambient fine particulate matter (PM _2.5 ) concentrations and daily COVID-19 incidence in Abidjan, Côte d’Ivoire, during the first year of the pandemic (March 2020–March 2021). Empirical evidence on environmental determinants of COVID-19 dynamics remains limited in African cities, despite persistently high levels of urban air pollution. Daily COVID-19 case data were analysed together with in situ measurements of PM _2.5 and meteorological parameters. Temporal associations were first explored using descriptive statistics and lagged Spearman correlations for delays ranging from 0 to 14 days. Non-linear and delayed relationships were then quantified using a generalized additive model (GAM) including environmental predictors at a fixed lag identified from the temporal analysis. COVID-19 incidence exhibited three major epidemic waves over the study period. PM _2.5 concentrations showed significant positive correlations with daily COVID-19 cases across all investigated lags, with a dominant peak at approximately 8 days. The GAM revealed a strong and non-linear exposure–response relationship between PM _2.5 and COVID-19 incidence. Relative risk increased progressively with PM _2.5 levels and reached a maximum of approximately 2.0 at concentrations around 40 µg m ^-3 , indicating a doubling of daily COVID-19 incidence compared with low-exposure conditions. Meteorological variables showed weaker and more complex associations, while the PM _2.5 effect remained robust after adjustment. These findings provide rare city-scale evidence that ambient fine particulate matter acted as a significant environmental cofactor of COVID-19 dynamics in a West African megacity. They highlight the potential role of chronic urban air pollution in amplifying population vulnerability to respiratory epidemics and underline the importance of integrating air quality considerations into public health surveillance and epidemic preparedness strategies in rapidly urbanizing African cities.