Is Switzerland facing a serious flu wave? This is what the signs look like

It’s winter in Australia, while it’s summer here. Because influenza viruses mainly circulate in winter, the flu season starts six months earlier there than here. Infectiologists in the Northern Hemisphere use this. “The flu activity in the Southern Hemisphere in the summer months provides an indication of the flu activity in the Northern Hemisphere in the following winter,” said Stefan Kuster, head of infectious diseases at St.Gallen Cantonal Hospital.

“Based on the viruses circulating in the Southern Hemisphere and the composition of the flu vaccination, it is possible to better estimate how good the protective effect of the flu vaccination could be in the Northern Hemisphere.”

The flu season in Australia was intense this year and started earlier than normal. The Southern Hemisphere peaked in late June and was similar to 2019. And 2019 is considered Australia’s strongest flu year. So you could easily assume that there is also a threat of a strong flu wave in the Northern Hemisphere. Professor Jan Fehr, an infectious disease specialist at the University of Zurich, says: “This cannot be deduced 1:1. Many factors influence an infection process and vary greatly from region to region.”

For example, the time of the start of the cold season and then immunity against influenza and other respiratory viruses play a role. This immunity is also related to the strictness of the Covid-19 measures in previous years. Because these have led to social distancing and hand hygiene due to changes in people’s behavior. During the pandemic, there were far fewer flu cases in Switzerland (see graph) and worldwide.

These measures are over and Fehr says: “I assume that regional differences will increase again after the Covid pandemic.” According to the university professor, the pandemic was a “level change” as almost all countries worldwide have taken measures to reduce the infection of Sars-CoV-2. These measures also worked against influenza or RS viruses. People’s immune systems came into less contact with viruses and therefore natural immunity was built up less.

“This synchronization no longer exists,” says Fehr. Unlike Australia, Switzerland relaxed measures earlier last year. This could give us better immunity against flu and other respiratory viruses than in Australia. “Whether this is the case remains to be seen,” says Fehr. In short, he says a high number of flu infections are likely, but not as pronounced as in Australia. We don’t know for sure.

It was striking that in Australia children were mainly affected by the flu. That is why people there spoke of a ‘friendly flu’. A striking number of children had to be admitted to hospital with a flu infection. Three factors came together, Fehr says. Firstly, due to the protective measures during the pandemic, the children hardly came into contact with flu or other respiratory viruses. They therefore lack partial immunity.

“At the same time, children are generally not vaccinated and thirdly, the flu virus, like other respiratory viruses, can circulate particularly quickly in children,” says the infectiologist from the University of Zurich. Children often have much closer contact than adults during play.

Adults can prevent flu with a vaccination. Flu vaccination has been possible in Switzerland since this week. “For people at increased risk of complications, the annual flu vaccination is recommended. This includes people over 65 and people with chronic diseases as well as pregnant women,” said Simon Ming of the Federal Office of Public Health (BAG).

The flu vaccine must be adjusted every year to new virus strains, because flu viruses, like coronaviruses, are constantly changing. However, the World Health Organization (WHO) determined in February which virus strains should be taken into account in the new flu vaccination for the Northern Hemisphere – i.e. before the flu season in Australia.

“Of course we would be happy if we could only develop the vaccine once it was clear which flu strains were relevant in the season,” says Professor Fehr. The problem, however, is that the development is very complex and there are several months between production and vaccination. “It would be ideal to have a vaccine that is no longer so dependent on different strains. Intensive research is being conducted into this.”

It is therefore impossible to predict how high the hit rate of the flu vaccine will be. “Every flu season is very different. “We didn’t do too bad last year,” Fehr said. And BAG’s Ming adds that last season the circulating type A strains were largely covered by the recommended vaccines. A year earlier, this worked less well than last season, while in the winter of 2018/19 the virus strains were almost completely covered and the vaccination therefore had the maximum effect.

The RS viruses were talked about more than the flu. Switzerland is experiencing an unusually early and strong RSV season. As a result, record numbers of hospital admissions were recorded in children’s hospitals in Switzerland. This raises the question of whether RSV is on the rise again. “As far as I know, there are no such signals,” says Stefan Kuster. However, RSV is not reportable and therefore a detailed overview is lacking.

“Currently we have very few RSV children in the Children’s Hospital of the University of Zurich. “It is still very quiet in this regard throughout Switzerland,” says infectious disease specialist Fehr. On the website of the National Reference Center for Influenza, only two positive detections of RSV are reported in week 41 out of a total of 42 samples analyzed.

It is difficult to make a prediction for the coming winter. “But because we know about RSV from pre-pandemic times that there is often a stronger epidemic every other year and quieter years in between, I assume that RSV numbers this year will not be as high as last year.” In addition, many children had built up some immunity against RSV over the past year. (aargauerzeitung.ch)