Research shows that there are more cases of COVID-19 as temperature and humidity drop. A recent study indicates more severe cases in cold and dry weather. Do these indications suggest that COVID-19 is a seasonal virus? Experts disagree.
Why did the United States have the most cases during a hot, humid summer? Studies conducted in 2003 on the first SARS-CoV show that weather is an important factor in the spread of the virus, namely:
Humidity and precipitation:
Laboratory studies and the number of new cases of patients with COVID-19 show a high impact of humidity on the spread of SARS-CoV-2 virus. In the laboratory, the SARS-CoV-2 virus was stable at a relative humidity of 53% and a room temperature of 23 ° C. The virus had not degenerated much even after 16 hours and was more robust than MERS and SARS-CoV. This explains its contagious power in the air.
Laboratory studies do not necessarily predict how a virus will behave in the real world. However, a study conducted in 17 cities in China (with over 50 cases of COVID-19) found a link between increases in humidity and reductions in COVID-19 cases. The team measured the humidity as absolute humidity or the total amount of water in the air. For every gram per cubic meter (1 g / m3) increase in absolute humidity, there was a 67% reduction in COVID-19 cases after a 14-day gap between the increase in humidity and the number of cases.
Between January and March 2020, the affected cities had low average temperatures of 5-11 ° C, and low absolute humidity of 4-7 g / m3, which is why the study authors conclude that these findings are: "Consistent with the behavior of a virus seasonal respirator. ”
The links between COVID-19 cases and temperature are less conclusive. Studies in China have not found an association of the virus with ambient temperature. However, higher temperatures are associated with a lower number of cases in Turkey, Mexico, Brazil and the United States, but there seems to be a threshold. This is consistent with laboratory studies showing that the SARS-CoV-2 virus is extremely stable outside the body at 4 ° C, but increasingly unstable at temperatures above 37 ° C.