H1N1 mutation and early flu season prompt researchers to reconsider shots

A variant of the H1N1 influenza virus is dominating the early Northern Hemisphere flu season, prompting public-health researchers to reconsider when individuals should receive their annual flu shots. Data show that influenza positivity rates are unusually high for this time of year in regions such as the United Kingdom and the West Coast of the United States, while outbreaks forced school closures in Japan during August and early September.

If cases on the West Coast continue to rise at their current rate, it would mark an incredibly early start for the United States, according to University of Pennsylvania virologist Scott Hensley. The influenza subtype driving most of these early American cases is H1N1, unlike last year when H3N2 dominated. Sequencing data from these early cases have revealed an emerging mutation in H1N1 that is drawing concern from specialists.

Early US West Coast Outbreaks and H1N1 Dominance

During the week ending September 26, H1N1 accounted for 96% of positive influenza cases where subtyping was performed in the United States, according to US Centers for Disease Control and Prevention data. H3N2 accounted for nearly 4% of cases, while influenza B was not detected. This shift contrasts with the previous year, when a new H3N2 variant called subclade K emerged and became globally dominant due to mutations that increased human vulnerability.

Researchers caution that these findings stem from a relatively small number of positive tests compared with peak season volumes, making it too soon to predict the outbreak’s overall trajectory. University of Oxford epidemiologist James Hay noted that an early start does not necessarily mean a more severe season. Nevertheless, Johns Hopkins University researcher Caitlin Rivers wrote in her newsletter, Force of Infection, on September 27 that there is something afoot.

G155E Mutation Appears in Seattle H1N1 Samples

The specific mutation worrying researchers in the current H1N1 strain is G155E. University of Washington virologist Alex Greninger reported that his laboratory detected G155E in 13 of 17 H1N1 samples collected from hospitals and clinics in Seattle over the past few months that had complete enough genetic sequences for specific identification.

This mutation was previously flagged in an analysis led by Fred Hutchinson Cancer Center virologist Jesse Bloom, posted on the preprint server bioRxiv ahead of peer review. Bloom and his colleagues tested blood samples from 260 individuals in Australia and the United States against 148 circulating influenza A viruses. We saw that a number of strains which have the G155E mutation are, in some cases, less well recognized by pre-existing human antibodies, Bloom stated, noting that antibodies from teenagers and young adults were especially inept at recognizing the variant because many in these groups lack prior exposure to similar H1N1 characteristics.

Shifting Vaccination Strategies Amid Uncertain Trajectories

The unusual timing and emerging viral characteristics are leading some public-health experts to alter their personal protection plans. Rivers stated that while she would typically wait until mid-to-late October to receive a vaccination in anticipation of a December or January peak, she is now considering getting a jab as soon as possible.

Whether early regional surges will translate into a broader, continent-wide epidemic or how effectively current seasonal vaccines will neutralize strains carrying the G155E mutation remains to be determined as virologists continue sequencing incoming patient samples.

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