In Germany, a second flu wave has begun this season. According to the definition of the Robert Koch Institute (RKI), the beginning is retrospectively dated to the week until 5 March, as shown by the weekly report on acute respiratory diseases on Wednesday evening. The second flu wave was triggered by the circulation of influenza B viruses. Thus, the flu season in Germany continues unusually.
This season, according to RKI data, there was already an exceptionally early flu wave before the turn of the year. This was caused by influenza viruses of subtype A(H3N2). This wave was slowed down relatively quickly by the Christmas holidays, so that the criteria for the end of the wave were already met in the first calendar week of 2023. Compared to the beginning of the first flu wave, influenza activity is currently increasing more slowly and less.
Figures based on samples from doctors' offices
In the previous seasonal flu waves, there was often an increase in the proportion of influenza B viruses after the circulation of influenza A viruses at the beginning of the wave. "But this went smoothly into each other," the RKI had recently explained at the request of the German Press Agency. Influenza B then led to an extension of the flu wave, but not to an interruption with such a significant drop in influenza activity as in this season around the turn of the year.
The assessment is based on results from a monitoring system in which samples from people with acute respiratory diseases are examined. It routinely looks for various pathogens, such as rhinoviruses, Sars-CoV-2 and influenza.
The annual flu wave began in the years before Corona, according to RKI usually in January and lasted three to four months. In the past two seasons, however, the pandemic and the measures taken against it changed the usual course considerably: In 2020/21, the flu epidemic failed worldwide. And even in 2021/22 there was no wave in Germany on the usual scale, the registration numbers went up only after the Easter holidays and thus very late.