Infections, flu and Co.: Is the immune system out of practice?

Almost everyone seems to be sneezing or coughing right now.

Infections, flu and Co.: Is the immune system out of practice?

Almost everyone seems to be sneezing or coughing right now. Also, there is always some nasty gastrointestinal virus. Some people wonder whether the immune system has forgotten all other pathogens in Corona times. Can this be?

Not again: every few weeks the children are ill - colds, gastrointestinal and so on. And some adults also report their impression of taking just about every cold with them at the moment. After two years with countless calls for action to avoid infection and with travel restrictions, a lot of home office and mask requirements, coughing and sniffling can actually seem unusual. Especially at this time of year. But is there more to it? Have our immune systems forgotten how to defend themselves against pathogens due to lack of activity?

Many diseases such as flu and whooping cough have become rare in the pandemic, says the chairman of the German Society for Infectious Diseases, Bernd Salzberger from the University Hospital Regensburg. At the beginning of 2021, an analysis by the Robert Koch Institute (RKI) on several notifiable diseases from tuberculosis to hepatitis E showed that between March and the beginning of August 2020 around a third fewer cases were reported than had been expected based on the previous year's values would be - except for Covid-19.

Respiratory diseases, for example, fell particularly sharply, which is also a result of corona measures such as masks and distance. But what is the situation now, since droplets and aerosols and thus many pathogens can often be transmitted between people again unhindered? If you look at data from the Influenza Working Group at the RKI, which, in addition to flu and Covid-19, also deals with common cold pathogens such as rhinoviruses, you will notice unusual developments.

Influenza viruses, for example, have only been on the rise in children since Easter - a time when the season is usually coming to an end. After the failed flu epidemic two seasons ago, the figures for 2021/22 still point to very restrained events overall.

The curve for the estimated rate of respiratory diseases as a whole in the population reflects this to some extent: since January it has been well above the 2021/21 season, which was very heavily influenced by Corona, but never reached the heights of the three seasons before the pandemic, in which otherwise the flu epidemic dominated. Instead, things now seem to be dragging on longer into the spring: for the past few weeks, the RKI has shown higher values ​​than at this time in the four previous seasons. However, general practitioners do not see a situation that is completely out of the ordinary.

"We are currently not observing any noticeable accumulation of respiratory diseases in general practices," said a spokesman for the German Association of General Practitioners. "The situation can vary from region to region, so that the general practitioners there treat a particularly large number of patients with corresponding symptoms." However, no clear trend can be identified nationwide.

But what is the truth of the much-voiced suspicion that the immune systems have been weakened by the pandemic or the corona measures? "The immune system is not a muscle: it does not recede when it is not used or when it is used less," says Carsten Watzl, Secretary General of the German Society for Immunology. The immune system has certainly been spared a bit over the past two years, but has not become superfluous. "Nevertheless, there was something to do: People come into contact with pathogens not only through the respiratory tract, but also through the skin or food, so that the immune system kicks in."

The immunologist has a different explanation: for some colds, you simply have to do it every two or three years. “Seasonal corona viruses are an example of this. Anyone who has missed them in the past two years can now catch several colds in a row. This is a catch-up effect, similar to what was seen with RSV infections in children last autumn.” RSV stands for Respiratory Syncytial Virus. It can cause severe pneumonia and is particularly dangerous for premature babies, infants and young children. A big wave among children had also appeared in other countries.

Experts also see - also a consequence of the pandemic - increased attention to the topic and possibly a changed subjective perception as a result. "During the pandemic, many of us got used to not having colds for a long time at a time. Even before that, it was always the case that we were affected," says Watzl.

The unusual outbreak of monkeypox currently being observed cannot be explained by immune systems in western countries that are supposedly weakened by the pandemic, says Watzl. "It is rather the case that pathogens from the animal kingdom are spreading to humans more and more frequently." This is due to the fact that people are increasingly penetrating previously undeveloped areas - and to the numerous international travel movements. "We will see such diseases more frequently in the future. If you think of the emergence of Mers, Sars and Sars-CoV-2, monkeypox is rather harmless," says Watzl.

From the point of view of scientists, caution is advised in the coming autumn: “If we have not come into contact with influenza in these years, it is possible that the virus will “run away” from us in evolution, so we will eventually deal with a virus that we know less well," says Salzberger. But the immune system does not forget old encounters so quickly. Antibodies against influenza hardly decreased during the pandemic. Nevertheless: "Vaccination fatigue this autumn and winter would be negligent," emphasizes Salzberger. "Each influenza vaccination improves our immune response to an influenza infection and that is extremely important for high-risk patients."

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