Early Flu Season Is Here. What to Know About Mutated Virus H1N1

Key Points:

• The 2026-2027 flu season is starting earlier than usual, with rising cases reported in 44 states as of October 21, and moderate activity in Louisiana and Hawaii, primarily driven by a mutated H1N1 strain.
• The current dominant strain, H1N1 (the "swine flu"), has acquired a new mutation (G155E) that may help it evade pre-existing immunity, potentially leading to increased susceptibility, especially among young people.
• Flu activity indicators such as test positivity rates and outpatient visits for flu-like illness are higher compared to previous seasons at this time, although it remains too early to predict the overall severity of this flu season.
• Experts strongly recommend getting the 2026-2027 flu vaccine, which covers H1N1, H3N2, and influenza B strains, emphasizing that vaccination can reduce the risk of severe illness even if the circulating strain partially evades immunity.
• Antiviral treatments are available for those who test positive for the flu, especially important for high-risk groups, and should be started within 48 hours of symptom onset to be most effective.