New flu‑tracking method

Flu vaccines are picked months before winter, and a Fred Hutch team says it can now show, almost in real time, how well people’s antibodies still recognize the latest strains. (fredhutch.org) The method uses blood serum, the part of blood that carries antibodies, and tests it against a large panel of current flu virus surface proteins to see which strains are still blocked well and which are slipping past immunity. In a February 18, 2026 preprint, the team reported 27,409 neutralization measurements from 302 human serum samples tested against 57 H3N2 and 34 H1N1 influenza hemagglutinins representing viruses circulating in late 2025 and early 2026. (jbloomlab.org) Those measurements found lower antibody titers against the K subclade of H3N2 and the D.3.1.1 subclade of H1N1, two groups that had recently become dominant. The researchers also reported especially low titers against some K-subclade H3N2 viruses with extra mutations in antigenic regions, the parts of the virus antibodies target most directly. (jbloomlab.org) Seasonal influenza mutates fast enough that vaccine strains are reviewed twice a year, in September for the Southern Hemisphere and in February for the Northern Hemisphere. A 2025 Virus Evolution paper from the same group said manufacturers usually need about 8 to 12 months of lead time, which forces officials to make strain choices well before the next season starts. (academic.oup.com) Fred Hutch said Caroline Kikawa, a University of Washington Medical Scientist Training Program graduate student working with Jesse Bloom, produced more than 25,000 antibody measurements in under six months and shared them publicly. The center said those data were considered in the September 2025 decision for the 2026 Southern Hemisphere vaccine and in the early 2026 decision for the Northern Hemisphere’s 2026-2027 vaccine. (fredhutch.org) The World Health Organization said on February 27, 2026 that it had updated the 2026-2027 Northern Hemisphere vaccine recommendation after a four-day consultation of global surveillance data. The agency said a notably different H3N2 variant, J.2.4.1, also called subclade K, emerged in August 2025 and spread rapidly worldwide, becoming the majority of reported flu viruses across regions. (who.int) For the 2026 Southern Hemisphere season, the World Health Organization recommended trivalent vaccines with H1N1, H3N2, and B Victoria components, and said again that a B Yamagata component was no longer warranted. The same document shows why faster antibody readouts matter in practice: the strain list differs by vaccine platform, with one H3N2 recommendation for egg-based vaccines and another for cell-based, recombinant, or nucleic-acid vaccines. (who.int) United States regulators reviewed the same moving target in March 2026. A Food and Drug Administration briefing document for its March 12 advisory meeting said influenza A viruses, especially H3N2, dominated globally from September 2025 through January 2026 and that strain selection depends on surveillance, lab characterization, serology, vaccine effectiveness, and the availability of candidate vaccine viruses. (fda.gov) This is the second season in a row that the Bloom lab has published a large antibody map on the timetable used for vaccine selection. Its 2025 Virus Evolution study reported 26,148 neutralization measurements from 188 human serum samples tested against 140 contemporary H3N2 and H1N1 viruses to inform the September 2025 Southern Hemisphere decision. (academic.oup.com) The closing test for this approach is simple: whether health agencies can keep using fresher immunity data before vaccine deadlines pass. Fred Hutch said the team built the system for both hemispheres’ decision cycles, where a few weeks can matter as much as a few mutations. (fredhutch.org)