The new K strain presents a genetic particularity which differentiates it from the viruses of previous years. Doctors and authorities are monitoring her very closely.
The flu is gaining ground in France and all regions are in “red” (epidemic stage) on the map. Each year, the flu virus mutates slightly and comes in new forms (called strains), requiring an updated vaccine. Scientists are closely monitoring these developments to identify the dominant strains in order to best prepare the vaccine response. This season, it is the K strain, one of the sub-variants of the A(H3N2) influenza virus, which is worrying doctors and health authorities. The first genetic analyzes highlight that the K strain presents a genetic particularity (7 mutations) which differentiates it from the circulating strains of previous years. Public Health France insists that it is still too early to assess its precise impact.
In December 2025, the K strain is the majority genetic lineage among characterized H3N2 viruses, representing approximately 70% of the viruses sequenced since the start of surveillance, according to the latest Public Health France bulletin. Against the flu, vaccination remains the best defense: it greatly reduces the risk of serious forms, hospitalizations and death. The current vaccine is a trivalent vaccine which contains an A(H3N2) influenza strain, in addition to an A(H1N1) strain and a B strain. Theoretically, this vaccine therefore targets the right “family” of viruses, which is already a basis for protection. Despite everything, this vaccine could be a little less effective to specifically neutralize the K variant compared to the H3N2 strain which was used to manufacture the vaccine. To date, doctors say that it is still too early to know the exact impact of this delay on the real effectiveness of the vaccine in France, but the situation is being monitored very closely.
There are no new specific or unusual symptoms linked to the circulation of the K strain. It causes a classic flu syndrome which generally manifests itself suddenly and intensely with 3 symptoms: high fever (39°C or more often accompanied by chills), muscle aches and severe fatigue. Other likely symptoms that commonly accompany them are severe headaches, as well as dry cough and runny nose.
It is therefore not the nature of the symptoms which worries the health authorities, but rather the intensity of the circulation and the risk of serious forms in the elderly or immunocompromised people, raising fears of a rapid overload of Emergency services and a critical pressure on hospital capacities in the middle of winter.
Management of influenza, including the K variant, relies primarily on treating symptoms, as the infection resolves spontaneously within a few days for the majority of people. Paracetamol is to be preferred while respecting the maximum doses and the interval of 6 hours between doses. Non-steroidal anti-inflammatory drugs (NSAIDs) should be avoided unless advised by a doctor. You should drink plenty of water (or hot drinks) to avoid dehydration, especially if you have a high fever. Finally, sufficient rest is essential to allow the body to fight the virus.
