"Expect the unexpected!" What sounds like the slogan for an adventure trip is also a motto of influenza researchers.

Don't make predictions, don't rely on anything.

The seasonal virus flu is always good for surprises.

Sometimes it is mild, then again the virus has changed so much within a short period of time that the vaccine does not fit - and in the worst case many people get sick and die.

Expecting the unexpected seems to be the best strategy for the coming weeks.

Because this winter, two potentially dangerous respiratory viruses, influenza and SARS-CoV-2, may be circulating.

Experts warn of such a twindemic, even fearing the "perfect storm".

Pia Heinemann

Editor of Nature and Science

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In many countries in the northern hemisphere, masks and other corona rules were no longer required at the beginning of the cold season.

Pathogens spread largely unchecked, and this is also the case in Germany.

The weekly infection rates of all colds, including influenza, collected by the Robert Koch Institute are already higher than they were in the same period in the years before the pandemic.

In addition, the corona numbers are skyrocketing.

Apparently, according to the RKI weekly report, "a little slowed down transmission activity in the population".

The third fall of the pandemic has begun, and the coming weeks could be difficult across the country.

The return of the flu virus

Unlike the past two winter months, the other unpredictable is back: the influenza virus.

It was pushed back worldwide with the first lockdowns in 2020, masks, travel restrictions and hygiene measures have given it little chance of spreading until this year.

Influenza seasons were almost completely absent in both the southern and northern hemispheres.

In March, in the journal

Nature Communications

, a team led by the Australian influenza specialist Ian G. Barr understood in detail how devastating the corona measures were for influenza viruses: Individual strains such as the influenza B/Yamanata line seem to have spread as a result of the contact and Travel restrictions have been virtually extinct since April 2020, other virus lines such as influenza A H3N2 and H1N1 have been circulating with significantly reduced genetic diversity.

Small, regionally limited outbreaks only occurred in South and Southeast Asia, China and West Africa.

The corona measures have forced influenza viruses through a genetic bottleneck, the surviving lines, Barr's team predicts, will form the nucleus for future flu waves.

Does Omikron prevent a severe flu epidemic?

It is unclear whether the flu viruses will be more dangerous for humans this year.

"Influenza viruses are masters of evolution," says Gülsah Gabriel, who researches at the Leibniz Institute for Virology in Hamburg how adaptable and changeable influenza viruses are - and when they become dangerous for humans.

Because of the failed flu season, the immune system of many people was not refreshed by a natural infection, there is a risk of more severe courses.

"We don't know how good the protection is against the variants circulating this year."