"Superinfection" and Covid Why so many people are currently ill

The flu epidemic has Switzerland fully in its grip: influenza A dominates, RSV is on the rise and Covid-19 is also still present. Experts explain what is behind the rising number of infections.

Do you know someone who has the flu? Or are you lying flat in bed yourself? The flu is spreading. The number of sick people is rising. blue News asks experts why so many people are ill and what exactly is behind it.

Walter Zingg, head physician at the Clinic for Infectious Diseases and Hospital Hygiene at Zurich University Hospital, treats patients every day. He says: "At the moment, we are mainly seeing cases of influenza A." Although the wastewater measurements detect influenza A and B in similar quantities, the hospital is mainly treating patients with influenza A. SARS-CoV-2 also remains present, but to a much lesser extent than influenza. "The activity of SARS-CoV-2 in the canton of Zurich has decreased, so there are fewer Covid patients," says Zingg.

Another infection that is occurring more frequently is RSV (respiratory syncytial virus). "This virus plays a bigger role in children, but we see it less frequently in adults." Seasonal invasive pneumococcal infections also occur, sometimes as a bacterial "superinfection" in influenza patients, but not always.

Flu epidemic still on the rise, Covid on the decline

Also due to seasonal factors and comparable to the same time last year, Zingg has recorded an increase in patients with respiratory infections. "Currently mainly due to influenza. The overall activity of all respiratory pathogens has so far been within the range of what we saw at the turn of the year 2023/2024." However, the University Hospital Zurich is expecting a further increase in flu cases in January.

According to Zingg, viruses mutating is a natural process and a survival strategy. "Depending on the species, this happens more or less frequently." However, there is currently no evidence of highly genetically modified viruses.

Is it because of the immune system that so many people are ill? Zingg says no: "The immune system is not weakened. But we are still seeing some catch-up effects from the pandemic." The shutdown of society, especially the school closures, has successfully reduced exposure to SARS-CoV-2. However, this also affected other pathogens with which society had been living in equilibrium. Zingg says: "As a result, there were repeated outbreaks that were unexpectedly severe." For example, the recent cases of mycoplasma pneumonia, after this pathogen had completely disappeared during the pandemic or appeared during unusual seasons.

"The flu epidemic started three weeks ago"

The Federal Office of Public Health (FOPH) is also keeping an eye on the situation. A spokeswoman said on request: "The seasonal flu epidemic began three weeks ago. The proportion of influenza cases in the Sentinella reporting system has been rising steadily since then."

She continues: "The mandatory laboratory reports on influenza are also increasing in all age groups. An increase in the influenza viral load can also be observed in wastewater in most regions." The Covid-19 wave appears to have peaked. In wastewater, the mandatory reporting system and the Sentinella reporting system, there has been a downward trend in SARS-CoV-2 infections for a few weeks.

She says: "The most frequently detected SARS-CoV-2 variant in wastewater is XEC, which currently accounts for around half of the total SARS-CoV-2 viral load in wastewater." RSV activity has also been steadily increasing for three weeks.