The number of corona infections is growing explosively. At the same time, we are in the middle of the winter, which often means a peak in more innocent infectious diseases, such as the flu and the common cold. Can the arrival of spring put a brake on the spread of the corona virus? And will that be on time?
Climate conditions can influence the spread of viruses. This is partly due to how long a virus can survive outside the body of humans and animals. Some viruses are less transferable in warm outdoor air.
In addition, the relative humidity is important. When that layer is low, the microscopic droplets in which the virus particles float around remain in the air longer and can spread over greater distances. Dry air is a factor in buildings that are heated in the winter months.
See also: What can you do about the dry winter air in your house?
Many viruses are more active in cold months
But do these factors also apply to COVID-19? NU.nl spoke with three virus experts. They point out that viruses behave differently and that little is known about the COVID-19 virus. The available knowledge mainly comes from studies on viruses with similar properties.
"Other coronaviruses that cause respiratory tract infections in humans occur mainly in the winter months," says virologist Ab Osterhaus. "It is therefore possible that the COVID-19 virus also shows greater activity in the cold season."
Frank van Kuppeveld, professor of virology at Utrecht University, mentions a number of possible reasons why many viruses thrive better in cooler months. "In addition to the low humidity and temperature, there are indications that the resistance of mucous membranes in the nose is less when you breathe in cold air."
We are also more contagious in the winter, because we are often close together in small confined spaces, Osterhaus adds.
Few diseases in the tropics
Professor Louis Kroes of the Leiden University Medical Center also agrees that high air temperatures and humidity are likely to inhibit the virus.
"It is remarkable that almost no COVID-19 has been reported in Africa, Brazil and Indonesia." According to Kroes, there are two potential explanations for this: either the disease is not yet properly recognized, or the virus is actually less effective in humid tropical conditions.
"There are COVID cases from Singapore, but almost everyone lives in dry, cool air through air conditioning. Air conditioners seem ideal for virus transfer."
A seasonal brake cannot stop spreading
Van Kuppeveld specifically points to the earlier SARS virus from 2002, which he says "looks like a brother" to the new virus. "That virus has been shown to be more stable at lower temperatures and humidity. In addition, it is damaged in the open air by exposure to UV radiation from the sun."
But this research into SARS offers few guarantees for the short term: only above 25 degrees did temperature become a direct influence. Then it is already high summer in the Netherlands. And while exposed to UV, the SARS virus survived for less than an hour, but that is under (extreme) laboratory conditions. Not to be compared with a weak March sun.
The biggest concern, Kroes summarizes, is that it can take another two months for positive effects to occur. "The virological spring seems to come later than the meteorological spring."
Other virologists point out that the virus can spread to countries like Australia in our summer, and then return to the northern hemisphere in the fall.