Data from several Northern‑hemisphere locations indicate that influenza activity is beginning earlier than typical. Positive test rates for flu are unusually high for late summer and early autumn in the United Kingdom, on the United States’ West Coast and in parts of Japan, where August and September outbreaks forced some schools to close as they resumed after summer break.
Early indicators across the Northern Hemisphere
Virologist Scott Hensley of the University of Pennsylvania warned that, if the current trajectory on the West Coast continues, the United States could experience “an incredibly early season.” Researchers stress that the observations stem from a relatively small pool of positive tests compared with the volume seen at the peak of a typical season, so definitive predictions remain premature.
James Hay, an epidemiologist at the University of Oxford, cautioned that an early start does not automatically translate into a more severe flu season. Nonetheless, epidemiologist Caitlin Rivers of Johns Hopkins University noted in her 27 September newsletter that “there is something afoot,” prompting her to reconsider her personal vaccination timing. In a usual year she would wait until mid‑to‑late October for a flu shot, but the current data are leading her to contemplate getting vaccinated as soon as possible.
Dominance of H1N1 and a concerning mutation
Unlike the previous year, when H3N2 accounted for most cases, the current U.S. data show a sharp shift toward H1N1. For the week ending 26 September, subtyping revealed that 96 % of positive influenza A samples were H1N1, about 4 % were H3N2 and influenza B was not detected.
Sequencing of early H1N1 cases has uncovered a mutation designated G155E that is drawing attention from virologists. Alex Greninger of the University of Washington reported that his laboratory identified the G155E change in 13 of 17 H1N1 specimens that had sufficient genetic coverage. The samples were collected from hospitals and clinics in Seattle over recent months.
The mutation was previously highlighted in a pre‑print analysis led by Jesse Bloom at the Fred Hutchinson Cancer Center. Bloom’s team tested serum antibodies from 260 individuals in Australia and the United States against 148 influenza A viruses circulating by mid‑2026. Their results showed that strains carrying G155E were, in several instances, less effectively recognized by existing human antibodies, especially those from teenagers and young adults who have had limited prior exposure to similar H1N1 variants.
Implications for vaccination timing
The emergence of a potentially immune‑evasive H1N1 strain adds another layer of uncertainty to public‑health planning. Health officials typically recommend that most people receive the seasonal flu vaccine in October, aiming for optimal protection when the season peaks in December and January. However, the combination of early viral activity and the G155E mutation may encourage some clinicians and individuals to seek vaccination earlier than usual.
While scientists emphasize that early circulation does not guarantee a harsher season, the current observations underscore the importance of ongoing surveillance. Monitoring the spread of the G155E mutation and its impact on vaccine effectiveness will be critical as health agencies decide whether to adjust timing recommendations or update vaccine formulations for the 2026‑27 flu season.
As the situation develops, public‑health experts advise people to continue practicing standard preventive measures—hand hygiene, respiratory etiquette and staying home when ill—while staying informed about local vaccination guidance.
Helene Elliott is the Lead Science & Space Reporter at News Raise. She reports on aerospace missions, astrophysics discoveries, quantum research, and environmental technology.
