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The fight against the coronavirus will have an influence on the flu epidemic. This flu season could be delayed, or even absent, according to the example of the southern hemisphere countries. A consolation in this tense context, where a double infection would be an aggravating factor.
When the coronavirus pandemic broke out in March, the flu season had just started in the southern hemisphere. Countries like Australia and South Africa, however, did not see the usual wave of flu coming, and cases of flu remained at a historically low rate during the months of July and August in the heart of the southern winter.
Experts expect a similar effect in Switzerland. The precautionary measures adopted against Covid-19, such as wearing a mask, washing hands and sanitary distances, allow to reduce the transmission of droplets, the vector of the virus responsible for the flu.
“If we can control the incidence of Covid-19, it means that at the same time we will be able to control the incidence of the flu,” said Didier Trono, virologist and expert with the national Covid-19 task force, Tuesday at 7 pm: 30 Note that influenza causes between 400 and 1000 deaths every year in Switzerland.
Competition between viruses
Scientists are also wondering about the interactions between the two viruses. A preliminary study carried out in England between January and the end of April 2020 suggests that a flu infection would reduce the risk of Covid-19 infection.
Based on tests carried out on nearly 20,000 individuals for influenza and SARS-CoV-2, the researchers say the risk of being positive for Covid-19 drops by 58% when people have been tested positive for the flu.
A study to be taken with a grain of salt, as it has yet to be peer reviewed. However, it refers to a well-known phenomenon in virology, competition between viruses, which is driven by molecules called interferons.
“When a virus enters a cell, it causes them to produce substances which are released and which prevent other viruses from entering all neighboring cells. These interferons then establish a sort of firewall that makes the organism nonspecifically protected against. other viral infections, “explains Didier Trono.
Interferons can stay in the body for days or even weeks. Early results show that the flu vaccine could also activate this non-specific immunity against the coronavirus. But knowledge is still limited on this topic.
Risk of double infection
As for the possibility of simultaneous infection by the two viruses, it remains rare, especially if the flu virus is not very present. But the phenomenon is possible and leads to an aggravating factor. “Two recently published studies suggest that the death rate has doubled when there are two infections,” notes Blaise Genton. Head of the Infectious Diseases Department of Unisanté in Lausanne.
More than ever, the doctor recommends vaccinating the population. “The problem is that people with the flu have the same symptoms as those with Covid. These people will want to be tested and this will create a greater influx of patients. The sectors are already tight, they shouldn’t be overwhelmed.”
Due to strong demand this year, vaccine doses are being distributed as a priority to vulnerable people and healthcare workers. The rest of the population can be vaccinated from the beginning of December. “In general, flu epidemics occur between mid-December and mid-March. Knowing that it takes about two weeks to build immunity, this leaves a reasonable time,” concludes Blaise Genton.
Aurélie Coulon and Feriel Mestiri
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