New research shows that high temperature and high relative humidity significantly reduce the transmission of the COVID-19 coronavirus, while colder weather has the opposite effect.
This is bad news for South Africa, where temperatures and humidity are starting to decrease as winter approaches.
The study was conducted by four Chinese researchers who investigated the daily effective reproduction number of the virus for 100 Chinese cities with more than 40 COVID-19 cases.
The basic reproduction number (R) for each city was calculated, which showed that air temperature and humidity influence the transmission of COVID-19.
In cold and dry weather, the basic reproduction number of COVID-19 ranges between 2 and 3.
This means, on average, every person with the COVID-19 virus passes the disease to between 2 and 3 other people.
This value decreases significantly with an increase of temperature and humidity. An increase of one degree Celsius and one percent in relative humidity lower R by 0.0383 and 0.0224, respectively.
The reduction in COVID-19 transmissions in warmer temperatures held true even after controlling for population density and GDP per capita of cities.
Impact on South Africa
The reduction in COVID-19 transmissions in warmer weather is good news for China, the United States and Europe, which are going into summer.
The arrival of summer and the rainy season in the northern hemisphere can effectively reduce the transmission of COVID-19.
It is, however, bad news for South Africa. “Risks remain in some countries in the southern hemisphere like Australia and South Africa,” the researchers said.
The researchers produced two maps to show the difference in the expected transmission rates (R value) between March and July.
Green areas on the map (low R value) are good news, while red areas (high R value) are bad news.
South Africa turns from mostly green in March to mostly red in July, which illustrates the increased risk of COVID-19 in the coming months.