Effects of temperature and humidity on the daily new cases and new deaths of COVID-19 in 166 countries
Main result
On March 27, 2020, 509,164 confirmed cases and 23,335 deaths had been documented around the world. Italy, the United States, and Spain were the three countries with the largest number of COVID-19 cases outside China. In total, Italy, Spain, and Iran were the countries with the largest number of COVID-19 deaths outside China. Mean temperatures varied from -5.28 deg. C to 34.30 deg. C, and mean relative humidity varied from 11.39% to 88.42%.
Temperature and relative humidity were both negatively associated with daily new cases and deaths. An increase in temperature of 1 deg. C was associated with a reduction of 3.08% (95% CI: 1.53%-4.63%) in daily new cases and a reduction of 1.19% (95% CI: 0.44%-1.95%) in daily new deaths, while an increase of 1% in relative humidity was associated with a reduction of 0.85% (95% CI: 0.51%-1.19%) in daily new cases and a reduction of 0.51% (95% CI: 0.34%-0.67%) in daily new deaths.
The results were robust to different lag structures and sensitivity analyses were performed.
Takeaways
These results provide preliminary evidence that the COVID-19 pandemic could be partially suppressed with higher temperature and humidity.
Strength of evidence Moderate
- Proof prior to peer review
- Data were collected for 166 countries (excepting China) on March 27, 2020.
- This study was time series analysis.
- This study included variables that reflected economic level, medical conditions, population age, and population density to reduce confounding factors.
- The study used dates of daily situation reports of COVID-19 from the WHO instead of the date of appearance, which could introduce a bias because that time interval varies with medical conditions, politics, and diagnostic criteria of each country.
- The number of confirmed cases is inevitably underestimated, particularly in low-income regions, due to low coverage for detection of COVID-19.
- Political effects and measures to control transmission of COVID-19 were not evaluated in this study. However, certain measures, such as quarantine, can affect the prevalence of infectious diseases.
- Ecologically, errors could have been made by using the temperature and humidity of the capital cities to reflect the mean national temperature and humidity, and by using exterior exposure as an indicator of personal exposure.
Objectives
To examine the effects of temperature and relative humidity on daily new COVID-19 cases and deaths.
Method
Data on COVID-19 cases were collected in 166 countries (excepting China) on March 27, 2020. The data, which include daily new confirmed cases and deaths, were collected from daily situation reports of COVID-19 from the WHO.
Surveillance stations closest to the capital city of each country were used for daily meterological data, including daily mean temperature, mean dew point, and mean wind speed, and were obtained from the National Oceanic and Atmospheric Administration Center.
A log-linear generalized additive model was used to analyze the effects of temperature and humidity relative to the new daily cases and deaths of COVID-19, controlling for potential confounding factors such as wind speed, median national age of the population, Global Health Security index, Human Development index, and population density.
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