Climate and COVID-19 pandemic: effect of heat and humidity on the incidence and mortality in world's top ten hottest and top ten coldest countries.

OBJECTIVE: The COVID-19 pandemic has caused a global public health crisis with social, psychological and long-lasting economical damages. Weather-related dynamics have an impact on the pattern of human health and disease. The present study aimed to investigate the impact of heat and humidity on daily basis incidence and mortality due to COVID-19 pandemic in ten of the world's hottest countries compared to ten of the coldest ones.

MATERIALS AND METHODS: Worldwide, we selected 20 countries; 10 hottest countries with the highest temperatures and 10 coldest countries with the lowest temperature. The selection of the countries was based on the daily basis mean temperature from the date of appearance of the initial cases of COVID-19, Dec 29, 2019 to May 12, 2020. In the world's 10 hottest countries, the mean temperature was (26.31±1.51) and humidity (44.67±4.97). However, in the world's 10 coldest countries the mean temperature was (6.19±1.61) and humidity (57.26±2.35). The data on the global outbreak of COVID-19, daily new cases and deaths were recorded from World Health Organization, and daily information on temperature and humidity was obtained from metrological web "Time and Date".

RESULTS: In countries with high temperatures and low humidity, the mean daily cases incidence were (407.12±24.33); cumulative cases (9094.34±708.29); and cumulative deaths (452.84±43.30) were significantly low compared to countries with low temperatures and high humidity: daily cases (1876.72±207.37); cumulative cases (44232.38±5875.11); and cumulative deaths (2008.29±310.13). Moreover, COVID-19 cases and deaths per million population were significantly low in countries with high temperatures (cases 711.23, and deaths 16.27) compared to countries with low temperatures (cases 1685.99; and deaths 86.40). Furthermore, in hottest countries, a 1% increase in humidity reduced number of cases and deaths by (β = -5.40, p<0.001) and (β = -0.187, p=0.004) respectively. A similar trend was seen with a 1°C increase in temperature, reducing the number of deaths by (β = -1.35. p<0.001).

CONCLUSIONS: The results revealed a significant decrease in incidence of daily cases and deaths in countries with high temperatures and low humidity (warmest countries), compared to those countries with low temperatures and high humidity (coldest countries). The findings could be of interest to the policymakers and the health officials on the epidemiological trends of COVID-19 pandemic and weather changes.