Abstract
Seasonal variations in COVID-19 incidence have been suggested as a potentially important factor in the future trajectory of the pandemic. Using global line-list data on COVID-19 cases reported until 17th of March 2020 and global gridded weather data, we assessed the effects of air temperature and relative humidity on the daily incidence of confirmed COVID-19 local cases at the subnational level (first-level administrative divisions). After adjusting for surveillance capacity and time since first imported case, average temperature had a statistically significant, negative association with COVID-19 incidence for temperatures of −15°C and above. However, temperature only explained a relatively modest amount of the total variation in COVID-19 cases. The effect of relative humidity was not statistically significant. These results suggest that warmer weather may modestly reduce the rate of spread of COVID-19, but anticipation of a substantial decline in transmission due to temperature alone with onset of summer in the northern hemisphere, or in tropical regions, is not warranted by these findings.
Highlights
Pandemic COVID-19, caused by a beta-coronavirus named severe acute respiratory syndrome (SARS)-CoV-2 first identified in Wuhan, China [1], has spread rapidly
This study aimed to analyze seasonal variation in COVID-19 at subnational level, taking limitations of existing studies into account. This population-based open cohort study investigated the effect of weather-related variables on daily COVID-19 case counts at the beginning of the pandemic
Model comparison showed that the full model and the model including the temperature variables and confounding variables only provided a similar fit to the data (Table 2)
Summary
Pandemic COVID-19, caused by a beta-coronavirus named SARS-CoV-2 first identified in Wuhan, China [1], has spread rapidly. This spread was pronounced in temperate regions of the northern hemisphere, coinciding with winter [2]. There has been much speculation about whether warmer temperatures are associated with decreased COVID-19 transmission, similar to what is observed for many viral respiratory infections [6]. Decreased aerosol spread at higher temperatures is another possible mechanism, as observed for human influenza viruses [9], though the role of aerosols in SARS-CoV-2 transmission remains unclear [10,11,12,13]
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