Influenza cases have begun appearing on the West Coast about two and a half months ahead of the usual schedule, a timing not observed since the 2010 season, according to Dr. Michael Osterholm of the Center for Infectious Disease Research and Policy. While the Centers for Disease Control and Prevention (CDC) still classifies overall flu activity as low, it has recorded roughly 16,000 flu‑related hospitalizations and expects the numbers to rise as the virus moves into the Midwest and East Coast.
Unusual timing and a mutated H1N1 strain
Travel patterns may have played a role in the early start, but Dr. Amesh Adalja of Johns Hopkins Center for Health Security says there is no definitive explanation. The dominant strain this season is an H1N1 virus carrying the G155E mutation. Adalja notes that, to date, there is no evidence that the mutation increases disease severity, though it resembles features of H1N1 viruses that circulated before 2009.
Early research suggests that individuals under 25 have reduced immunity to this particular strain, potentially allowing it to bypass protection from previous infections or vaccinations. So far the season has seen one pediatric influenza‑related death—a school‑age child from outside the Denver metro area—and an estimated 24,000 flu‑related deaths nationwide, including 198 children.
According to Dr. Alex L. Greninger of the University of Washington, the severity of illness depends more on a person’s underlying health—such as limited cardiopulmonary capacity—than on the virus itself.
Vaccine match, new mRNA option, and timing
The seasonal flu vaccine was formulated before the G155E mutation emerged, making it a less precise match for the circulating virus. Nevertheless, experts stress that vaccination still offers substantial protection against severe outcomes. Osterholm likens the vaccine to a seatbelt, reducing the risk of hospitalization and death even when the match is imperfect.
Despite the United States’ recent departure from the World Health Organization, the CDC participated in the WHO’s February strain‑selection process, meaning the vaccine components used in the U.S. are identical to those administered in Canada and Mexico.
For the first time, an mRNA‑based flu vaccine, Moderna’s mFlusiva, is available to the public. It is recommended for adults aged 50 and older and has been reported to cause milder side effects than the mRNA Covid‑19 vaccines. Although mFlusiva was also produced before the mutation, Adalja hopes that mRNA technology will enable future vaccines to be updated closer to the start of flu season, improving match quality.
Because it takes roughly two weeks for the body to develop protective antibodies after vaccination, health officials advise people to get the shot now, before the holiday travel surge. Osterholm specifically urges those under 25 to act promptly. He also recommends receiving a Covid‑19 booster at the same time as the flu shot, noting that mild short‑term reactions are preferable to contracting influenza.
Guidance amid advisory turmoil
In 2025, the CDC’s traditional vaccine advisory committee was disbanded by Health Secretary Robert F. Kennedy Jr., and a federal court has paused the new panel’s activities. Consequently, the CDC is relying on last year’s recommendations, and the Advisory Committee on Immunization Practices no longer exists in its usual form.
Major medical societies—including the American Academy of Pediatrics, the American Academy of Family Physicians, the American College of Obstetricians and Gynecologists, and the Infectious Diseases Society of America—have issued coordinated guidance based on an evidence review by the Vaccine Integrity Project at Osterholm’s center. All four groups advise flu vaccination for everyone six months of age and older, including pregnant people at any stage of pregnancy.
Adalja suggests that the public look to these professional organizations rather than the CDC for the most reliable information, given concerns about potential political influence on CDC data. While the United States’ exit from the WHO did not affect the current vaccine composition, experts warn it could complicate responses to novel flu strains that emerge abroad.
Predicting the season’s trajectory remains difficult, though holiday travel typically amplifies transmission. Nonetheless, experts do not rule out a “normal” season in January and February. Until more data emerge, they emphasize classic preventive measures—vaccination, hand hygiene, masking with N95 respirators when ill, and staying home if symptomatic—as the best defense against influenza.
Helene Elliott is the Lead Science & Space Reporter at News Raise. She reports on aerospace missions, astrophysics discoveries, quantum research, and environmental technology.
