© Cottonbro Studios
October 30, 2026
Marianne Waldenfels
A new variant of the H1N1 flu virus is spreading. Early laboratory studies suggest that antibodies in teenagers and young adults may be less effective at neutralizing the altered virus. The reason could lie in their childhood encounters with influenza.
Find a DoctorSearch the network for suitable specialists and contact them directly
Flu cases in the US are rising unusually early, and schools in Japan have already had to close because of influenza outbreaks. A new and increasingly widespread variant of the H1N1 virus may be responsible. For Germany, the question is what to expect this winter — and how well the current flu vaccine holds up against it.
Flu activity in the Northern Hemisphere does not normally pick up significantly until late autumn. This year, however, the virus has been circulating earlier than usual in some countries. In the US, infection numbers have been rising since the end of August. Activity nationwide is still low, but above what is typical for this time of year.
Particularly notable is which pathogen is spreading. According to the US health authority CDC, in calendar week 41, 239 out of 241 more specifically identified influenza A viruses belonged to the H1N1 subtype. Last winter, H3N2 had dominated instead.
The new variant was also detected early in Japan. Health authorities there registered the relevant mutation as early as May 2026, and its spread has been accelerating since August, as Northeastern University reports.
The fact that flu viruses mutate is nothing unusual. But this time, virologists are interested not only in how quickly the pathogen is spreading — they also want to understand why some people's antibodies appear to be less well prepared for it.
The H1N1 virus circulating today is a descendant of the pathogen that triggered the swine flu pandemic in 2009. Since then, it has returned as a seasonal flu virus, changing continuously along the way.
One of these changes is designated G155E. It involves the substitution of a single building block in hemagglutinin, a protein on the surface of the virus. The pathogen uses this protein to attach to human cells, and it is also an important target for antibodies. If the protein changes at a critical site, antibodies may be less able to recognize the virus.
That appears to be precisely the case with G155E. The World Health Organization WHO is also monitoring the situation. According to its October report, H1N1 viruses carrying this mutation are spreading increasingly within the currently circulating virus lineage D.3.1.1.
Severe flu cases primarily affect older people and those with chronic illnesses. But with the new H1N1 variant, a portion of the younger generation — of all people — could be at a disadvantage.
This is suggested by a study by virologist Jesse Bloom and his team at the Fred Hutchinson Cancer Center in Seattle. The researchers examined 355 blood samples and tested how well the antibodies they contained could neutralize 148 different virus variants.
The result: while the antibodies of many people continued to recognize the altered virus well, their ability to neutralize it dropped by more than half in some of the samples. This effect was observed particularly frequently in teenagers and young adults between the ages of 15 and 25.
But why should their immune systems in particular be less well prepared for this change? One possible answer lies far back: in childhood.
When a child is exposed to a flu virus for the first time, the immune system memorizes certain characteristics of the pathogen. In later encounters with similar viruses, it preferentially draws on these early experiences. Researchers call this immunological imprinting.
Normally, this immunological memory is an advantage. But it can become a weakness if a virus mutates at precisely the site to which the immune system responds most strongly.
That may be exactly what happened with G155E. The swine flu pandemic of 2009 displaced the seasonal H1N1 viruses that had been circulating before it. People born after that therefore encountered different virus variants than older generations did.
The new mutation apparently affects a site on which the antibodies of certain younger age groups are particularly strongly focused. Older people, whose immune systems were shaped by other H1N1 viruses, may be better equipped to handle this change.
That early flu infections can influence the immune response for decades was already demonstrated by a study in the journal Science in 2016.
There is an additional factor: because H3N2 dominated in many places last winter, some younger people recently had little opportunity to refresh their immune response through an H1N1 infection.
The Seattle study has not yet been independently peer-reviewed. In addition, the researchers examined antibodies in the laboratory, not actual illnesses. Whether young people will therefore contract the new variant more frequently remains an open question. The highest risk of severe flu continues to lie with older people and those with chronic illnesses.
If existing antibodies are less effective at recognizing the altered virus, the question naturally arises whether the flu vaccine also offers less reliable protection.
The vaccines for the 2026/27 season were compiled before G155E became more widespread. The H1N1 strain included therefore does not fully match the new variants. However, that does not mean the vaccine is ineffective.
The US health authority CDC tested 88 current H1N1 viruses using antibodies raised against a reference strain from this year's vaccine. Of these, 82 — around 93 percent — were well recognized.
This is an encouraging sign, though with one caveat: the antibodies used came from experiments with ferrets. How well the vaccine actually protects people cannot be directly inferred from this. The CDC therefore considers it too early to assess the vaccine's effectiveness against the new variants.
Even if a vaccine does not prevent every infection, it can still protect against severe illness. It also targets other influenza viruses that may circulate during the course of winter.
While influenza activity in the US is increasing unusually early, no pronounced flu wave has yet been observed in Germany.
According to the current weekly report from the Robert Koch Institute dated October 28, 2026, the level of acute respiratory illness in the general population and in medical practices is moderate.
At present, rhino- and enteroviruses as well as parainfluenza viruses are the main drivers. Influenza viruses were detected in three percent of the sentinel samples examined. That said, the RKI has been observing a gradual increase in influenza activity over the past several weeks.
Whether G155E will also become more prevalent in Germany and lead to an earlier flu wave cannot be predicted at this stage. It is equally unclear whether the mutation will affect the number of cases or the severity of illness.
An early start to the season does not necessarily mean that an especially severe flu wave will define the entire winter.
The new findings do not change the fundamental vaccination recommendations for now. The Standing Committee on Vaccination (STIKO) recommends the annual influenza vaccination especially for people aged 60 and over, pregnant women, individuals with certain chronic conditions, and medical and nursing staff. Further details are provided by the Robert Koch Institute.
Since vaccine protection takes about two weeks to fully develop, autumn is a good time to get vaccinated.
Younger adults can also get vaccinated even if they do not belong to a high-risk group. Whether costs are covered depends, among other things, on the health insurance provider.
Anyone at increased risk of complications who develops typical flu symptoms should seek medical advice promptly. Antiviral medications work best when treatment begins as soon as possible after symptoms appear.
The new H1N1 variant illustrates that our immune system does not respond equally to every change in a virus. The flu viruses that shaped us in childhood could prove to be a decisive factor.
Whether young people will actually fall ill more frequently because of the G155E mutation remains to be seen. So far, there are indications from laboratory research, but no evidence of an increased risk of illness.
In Germany, flu activity remains low for now. The new variant does not change the vaccination recommendations at this time.
A nasal spray containing synthetic mebufotenin, a psychedelic also found in toad secretion, has shown promising results after just one dose in patients with treatment-resistant depression. Psychiatrist Prof. Dr. Andreas Menke explains what makes the substance different from other psychedelics and how significant the findings really are.
Christine Bürg & Marianne Waldenfels
An interview with
Prof. Dr. med. Andreas Menke
Liver metastases and liver cancer can be cured far more often today than ten years ago. Surgeon Prof. Carina Riediger explains why, what role alcohol plays, and why patients should see a specialized liver surgeon.
Christine Bürg & Marianne Waldenfels
An interview with
Prof. Dr. med. Carina Riediger, MSc
"Feel good, live better" – in this podcast episode with Prof. Dr. Katharina Storck, we talk about the nose and why we should pay more attention to it
Christine Bürg
An interview with
Prof. Dr. med. Katharina Storck
Radiofrequency, ultrasound, micro-coring: How much can the latest skin-tightening treatments achieve without surgery? Plastic surgeon Dr. Lukas Kohler explains which methods show promise, where they fall short, and why some treatments can even make the face look older.
Christine Bürg & Marianne Waldenfels
An interview with
Dr. med. Lukas H. Kohler
