NEW YORK--Doctors are urging Americans aged 6 months and older to get vaccinated against the flu after an unusual early rise in cases on the West Coast that virologists are still working to understand.
It could be the strain itself. The predominant flu strain this year is H1N1, which caused the 2009 swine flu pandemic and is now a standard part of the flu shot. But this year’s version of the virus has a new mutation called G155E.
People who have been previously exposed to H1N1, either through infection or vaccination, would only have some residual protection from the older versions, scientists say. "What people are a bit worried about is that the H1N1 strain this year hasn't been seen by a lot of younger folk, so it may be more severe in them," said Dr. Jennifer Duchon, a pediatric infectious disease expert at Mount Sinai Children's Hospital in New York, adding that her hospital has started to see some flu cases.
The 2026-2027 flu vaccines, approved by the FDA in August, target H1N1, H3N2 — the dominant strain last flu season — and one influenza B virus. While most children recover, flu can be deadly, especially for the very youngest and those with underlying health conditions.
Promotion of flu shots has been reduced under US Health Secretary Robert F. Kennedy Jr., a longtime anti-vaccine activist who has engineered an overhaul of long-standing childhood vaccine schedules. The American Medical Association recommends the shot for all people 6 months and older.
The vaccine's effectiveness fluctuates depending on how well it is matched months in advance to circulating flu strains. Over the past 10 years, it has been between 30% and 60% effective in reducing flu hospitalizations and deaths. Last year, an estimated 32 million Americans had the flu, 390,000 were hospitalized and 24,000 died.
Scott Hensley, a microbiologist at the University of Pennsylvania, said two of the three components of this year's vaccine appear to be very well matched to circulating flu strains. However, the H1N1 mutation might affect antibodies in younger people, and with flu season picking up steam, "it is probably a good idea to get vaccinated early," Hensley said via email.
Typically, flu cases start in Southern states and move north. This year, it's coming from the west, said Caitlin Rivers, a Johns Hopkins epidemiologist who tracks pathogens in a weekly newsletter called Force of Infection. “There's no clear reason to me why this would be the case,” Rivers said.
As last year was dominated by the H3N2, there could be an "immunological gap" because immunity to H1N1 virus is not as fresh. Or, it could be the new mutation, she said.
