Flu
The pandemic measures also caused a flu variant to die out completely
The genetic diversity of the influenza viruses was severely decimated under the measures taken to combat the pandemic. A variant has not been detected at all since April 2020. What does this mean for coming flu waves?
In the last two winters, people have rarely been in bed because of the flu – that will change again in the future.
Before the corona pandemic, flu waves were our annual companion. Almost every winter there was an epidemic caused by influenza viruses. The pandemic measures have not only contained Sars-CoV-2, there have also been remarkably few cases of flu in the last two years.
“Primarily, the last two years have shown that influenza is transmitted by droplets and could be easily controlled with a surgical mask and social distancing,” says infectiologist Christoph Fux from the Cantonal Hospital in Aarau. According to Fux, it would therefore be important to resort to such behavioral measures in order to contain a future wave of flu.
A subspecies of the flu virus has been eradicated
The influenza viruses that affect humans are divided into influenza A and influenza B. Both species are further categorized into subtypes. Influenza A subtypes are given names like H1N1 in swine flu. Influenza B is divided into lineages and named for where they occur.
Like now a research team around Vijaykrishna Dhanasekaranum in an article shows, which was published by Nature Communications, no influenza B virus of the Yamagata line has been detected since April 2020: the hygiene and contact measures have probably caused it to die out. In another important B line, the Victoria line, only one variant has survived. And numerous variants of influenza A have also become extinct.
It was to be expected that the measures would also have an impact on influenza: influenza is much less contagious than Sars-CoV-2. The R value, i.e. the number of people an infected person infects on average, is only 2. In the case of omicron, on the other hand, the R value is comparable to that of measles, i.e. between 12 and 18. (Calculations of the RKI here)
Weakened immunity to influenza viruses
The low flu numbers since 2020 may have led to poorer immunity in the population. The BAG does not expect it, as it communicates on request. Infectiologist Christoph Fux, on the other hand, is more cautious: “The immune system has not been trained for influenza for two years. If the next flu virus is also a really new variant, we have to expect a more severe flu season.”
Such a thing can still occur, especially a recombination of the main strains, as infectiologist Fux points out. Because these continue to happen in Asia, where people get too close to pigs and chickens. “As soon as travel starts again, this risk will increase again.”
The effect is even more likely in children under the age of two: Since infants and small children have not yet been able to build up immunity due to the pandemic, three age groups are now coming into contact with the virus at a time. Therefore, more infections must be expected next winter. The disease should not be more severe because of this.
Difficulties in vaccine production
While the flu is just a nuisance to most, it can pose a real threat to at-risk groups. Risk factors are – similar to Covid-19 – age and previous illnesses. To help these groups, a vaccine is developed each year to protect against the likely most common influenza subtypes.
The current situation is a challenge for the development of vaccines. Because according to the study mentioned above, the different strains of influenza are not as globally distributed as before the pandemic. Instead, there are regional outbreaks. This makes it difficult to predict which virus variants will dominate in the next wave and should be combated with vaccinations.
Because of the presumably reduced immunity, a good vaccine that works against all flu variants would be all the more important. Advances in research give hope for such a universal vaccine, also thanks to mRNA vaccines.
Until then, the remaining strands must be closely monitored in order to be able to react to them at an early stage.