This year's flu shots are likely to struggle against the ‘Super-K’ strain

Embargoed until: Publicly released: 2026-03-10 02:05

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Flu jabs in the US this season have been less effective against a particularly fast-moving flu strain now spreading in Australia, according to US research. Influenza A(H3N2) subclade K (J.2.4.1) - known as 'Super K' - is spreading faster and earlier in Australia than during typical flu seasons, after a dominant tour of the US in their winter months. The researchers assessed the antibody responses of 46 people who received a flu shot in late 2025 against a series of strains, including Super K and the strains the vaccine was developed to target. They say the samples showed a weaker antibody response to Super K compared to other strains, and it also appears that Super K can partially evade immunity from prior infection with similar flu strains. The researchers say there was still a modest response to Super K, so while flu shots were less effective than normal, they still likely offer some protection against it.

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Journal/
conference: JAMA

Research:Paper

Organisation/s: Harvard Medical School, USA

Funder: Dr Simon reported receiving a National Institutes of Health (NIH) contract (75N93021C00014). Dr van Bakel reported receiving an NIH contract (75N93021C00014). Dr Mostafa reported research collaboration with Hologic, QIAGEN, and Diasorin; receiving honoraria from bioMérieux, Bio-Rad, and Diasorin; and an NIH contract (75N93021C000045). Dr Pekosz reported receiving an NIH contract (75N93021C000045). Dr Collier reported having contracts with Pfizer and Sanofi outside the submitted work and receiving a Massachusetts Consortium on Pathogen Readiness Award and a William F. Milton Fund at Harvard University Award during the conduct of the study. Dr Barouch reported receiving grants from MassCPR during the conduct of the study; funding from the Massachusetts Consortium on Pathogen Readiness and philanthropic sources; grants from Biomedical Advanced Research and Development Authority, Defense Advanced Research Projects Agency, Gates Foundation, HenryM. Jackson Foundation, MassCPR, National Cancer Institute, National Institute of Allergy and Infectious Diseases, Ragon Institute, South African Medical Research Council,Walter Reed Army Institute of Research, Alkermes, CureVac, Gilead, Gritstone, GSK, Hookipa, Intima, Janssen, Legend, Leyden Labs, Musk Foundation, Novavax, Pfizer, Pharm-Olam, Sanofi, SIGA, and Zentalis; and personal fees from Avidea, Bavarian Nordic, Celsion/ Imunon, Laronde, Meissa, SQZ, Sterne Kessler, and Vector Sciences outside the submitted work. No other disclosures were reported.

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