Universal flu vaccine could eliminate annual doses

The seasonal flu vaccine is one of the best-known examples of the limitations of conventional vaccinology. Each year, the World Health Organization convenes experts to predict which influenza strains will circulate in the next season, and manufacturers produce a vaccine adjusted to that prediction. The system works when the prediction is correct and fails when the virus mutates in unexpected directions, as happened in the 2014-2015 season when vaccine efficacy dropped to 19%.

The universal vaccine seeks to solve that problem by attacking parts of the virus that do not change from one strain to another. Hemagglutinin, the protein the virus uses to attach to human cells, has a "stalk" region that is highly conserved across different strains and subtypes. If the immune system learns to recognise that stalk region instead of the "head" that changes each season, a single vaccine could generate protection against multiple variants of the virus over time.

The most advanced clinical trials in this field — including candidates from the National Institutes of Health, Pfizer and other laboratories — showed that it is possible to generate neutralising antibodies against conserved regions of the virus. Protection demonstrated in phase 2 does not guarantee commercial efficacy in phase 3, but data published between 2021 and 2024 is the most promising this field has produced. If phase 3 trials confirm efficacy, the public health impact would be significant: not only would it eliminate the need to vaccinate annually, but it would improve preparedness against influenza pandemics caused by new strains.