The joint impact of temperature, humidity, and air pollution on COVID-19 incidence: a multi-country time-series study in 439 cities
Wagatsuma, Keita Feurer, Denise Yu, Wenhua Xu, Rongbin Riffe, Tim Kniffka, Maxi Stella Acosta, Enrique Armstrong, Ben Mistry, Malcolm Lowe, Rachel
Wagatsuma, Keita
Feurer, Denise
Yu, Wenhua
Xu, Rongbin
Riffe, Tim
Kniffka, Maxi Stella
Acosta, Enrique
Armstrong, Ben
Mistry, Malcolm
Lowe, Rachel
Series / Report no.
Open Access
Type
Journal Article
Article
Article
Language
en
Date of publication
2026-01-24
Year of publication
Research Projects
Organizational Units
Journal Issue
Title
The joint impact of temperature, humidity, and air pollution on COVID-19 incidence: a multi-country time-series study in 439 cities
Translated Title
Published in
Environ Int 2026; 208:110090
Abstract
Several studies have explored the short-term effects of environmental stressors on coronavirus disease 2019 (COVID-19) transmission and severity. However, evidence on the interactive effects of meteorological conditions and air pollution remains limited and geographically variable. We therefore aimed to quantify the independent and interactive effects of short-term exposure to humidex, a composite index of temperature and relative humidity, and fine particulate matter ≤ 2.5 μm (PM) on daily COVID-19 incidence across multiple cities and in multiple countries. Daily time-series data on confirmed COVID-19 cases, meteorological factors, and PM concentrations were collected from 439 cities in 22 countries during January 2020-August 2022 as part of the Multi-Country Multi-City Collaborative Research Network. A two-stage design was applied: first, city-specific quasi-Poisson models with distributed lag non-linear models estimated exposure-response associations; second, multilevel random-effects meta-analyses pooled city-specific estimates. Effect modification by PM was assessed using a product term between non-linear humidex function and linear PM function. Approximately 95.1 million confirmed COVID-19 cases were analyzed. Lower humidex values (0.1 °C versus 15.1 °C) were associated with increased daily cases (relative risk [RR]: 1.1192, 95% confidence interval [CI]: 1.0214-1.2262). A 10 μg/mincrease in PM over the current and preceding 2 days was associated with a modest increase in daily cases (RR: 1.0079, 95% CI: 1.0001-1.0161). No statistically significant interaction between humidex and PM was observed. Short-term exposure to cold-dry conditions and elevated PM independently increased COVID-19 incidence, highlighting the need to consider both thermal environment and air quality when designing climate-resilient public health responses. These findings enhance understanding of how climate-related environmental stressors influence COVID-19 transmission.