West Coast flu cases rise months earlier than usual
Flu activity is rising unusually early across parts of the US West Coast, months before infections typically accelerate in December and peak in February. California’s influenza test positivity rate reached 9.65% by 10 October, compared with just over 1% at the same point in each of the previous two seasons. Utah recorded 242 influenza A cases by 11 October, up from 10 a year earlier, while central Oregon has also reported a surge.
Health experts have linked the early start to a mutation of the H1N1 influenza A strain associated with the 2009 swine flu pandemic. H1N1 accounted for 242 of the 300 influenza viruses reported so far by public health laboratories to the Centers for Disease Control and Prevention.
The FDA-approved 2026–27 vaccines target H1N1, H3N2 and one influenza B virus. University of Pennsylvania microbiologist Scott Hensley said two of the three vaccine components appear well matched to circulating strains, although the H1N1 mutation could affect antibodies in younger people. He advised early vaccination as infections increase. The American Medical Association recommends flu shots for everyone aged six months and older, noting that vaccination can reduce severe illness and hospitalization. The rise comes as promotion of flu shots has been reduced under US health secretary Robert F Kennedy Jr, a longtime anti-vaccine activist.
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