It is spring, temperatures are rising and the risk of colds is decreasing. Is the coronavirus now also weakening? Not necessarily, say scientists. A clear forecast is difficult.
Many people expect the coronavirus to weaken in spring and summer.
But this does not necessarily have to be the case, as the example of Spain shows.
According to experts, it is still far too early to give the all-clear.
“The seasonality of viruses that are spread via the respiratory tract is extremely complex,” says Ulf Dittmer, director of the Institute for Virology at the University Hospital in Essen. “It cannot be tied to individual factors.” After all: The Robert Koch Institute assumes that Sars-CoV-2 will spread better in the colder season. The transmission dynamics tend to weaken in summer.
“The fact that we had such a relaxed summer in 2020 probably had to do with the fact that our case numbers remained below a critical threshold in the spring,” said Christian Drosten, head of virology at Berlin’s Charité, to Spiegel. “But that is no longer the case.” In Spain, for example, the number of cases rose again in the summer after a lockdown – despite the heat.
UV radiation can damage viruses
According to the virologist Stephanie Pfänder from the Ruhr University Bochum, environmental influences can influence the stability of coronaviruses and also affect aerosols or droplets. According to Dittmer, the virus envelope is particularly stable at a temperature of around ten degrees. “The warmer it gets, the more the stability decreases,” explains the virologist. UV rays also act on the virus. They can attack the viral nucleic acid and damage the genetic information. “You can roughly say that UV radiation is able to inactivate the virus,” says Pfänder. The viruses are then no longer infectious.
The virus also affects the humidity. This is what studies on indoor transmissions suggest. According to the Leipzig aerosol researcher Ajit Ahlawat and other researchers from the Leibniz Institute for Tropospheric Research, the risk of infection inside is lower than normal when the air humidity is higher. With dry air, the nasal mucous membranes would also become drier and more permeable to viruses. “In summer, our immune system is better at fighting off new germs quickly and efficiently. This also applies to Sars-CoV-2, ”says immunologist Eva Peters. How much vitamin D helps against the virus, however, is controversial.
Mutants make predictions difficult
“We know from coronaviruses that the R-value, i.e. the rate of reproduction of the virus, drops significantly in spring and summer due to these factors,” says Dittmer. “So at least by a factor of 0.5, maybe even more.” However, the experts also point out that virus mutations are currently making forecasts difficult. The benefits that spring brings could be “eaten up” by the more infectious mutants, says Dittmer.
The seasonal effects could then possibly not be sufficient for the R-value to fall below the threshold of 1 in the long term, above which the pandemic subsides. Pfänder assumes that the warmer season of the year could already contribute to slowing down the transmission dynamics. “The occurrence and spread of mutants is actually a factor that is unpredictable.”
(DPA / wall)