Study Suggests COVID-19 Spreads Faster in Winter, May Be Seasonal in Northern Regions

Researchers from the University of Maryland School of Medicine started from a comparison: 42 potentially affected people in eight cities with a large number of cases, namely Daegu in South Korea, Madrid in Spain, Milan in Italy, Paris in France, Qom in Iran, Seattle in the United States, Tokyo, Japan; and Wuhan in China. Result: these coronavirus breeding grounds were located on a similar northern latitude band. Similarly, they had the same degrees of temperature and low humidity between January and March.

Based on climate data from the European Center for Medium-Range Weather Forecasts ERA-5, this study also allowed researchers to discover that Covid-19 had thrived between November and March in the eight cities studied, all of which were located on a latitude band between 30°N and 50°N. Conversely, the virus did not spread nearly as quickly in cities south of this band like Bangkok, which is located at 13.7°N.

The average temperature in Wuhan in January and in the seven other cities in February was between 4°C and 9°C, and the average temperatures were generally the same in all these cities 20 to 30 days before their first Covid-19 related death, ranging from 3°C to 9°C, the report notes.

"We believe the virus behaves like a seasonal respiratory virus. This means the virus has temperature and humidity requirements that facilitate its transmission," said Dr. Mohammad Sajadi, associate professor at the Institute of Human Virology at the University of Maryland School of Medicine. Impaired immunity during the winter months could also contribute to the rapid spread of the virus, the study suggests.