Neutralization of H5N1 by seasonal flu vaccines, UK 2021–2024
A study published in Emerging Infectious Diseases investigated the potential cross-protection conferred by seasonal quadrivalent influenza vaccines (QIVs) against highly pathogenic avian influenza A(H5N1) viruses, specifically those of clade 2.3.4.4b. Despite initial expectations, the study found limited evidence that QIVs elicit significant neutralizing antibody responses against these H5N1 strains in humans, particularly within the examined cohort of primarily healthy adults. The immunity induced by seasonal vaccination appears insufficient to confer robust or durable protection against severe H5N1 disease.
Furthermore, the study demonstrated that QIVs do not generate strong cross-neutralization in vitro against contemporary H5N1 viruses. While transient protection has been noted in animal models, no in vivo challenge studies have confirmed effective cross-protection.
Collectively, the findings suggest that current seasonal quadrivalent influenza vaccines are unlikely to provide adequate protection against severe H5N1 disease, particularly in vulnerable populations during widespread outbreaks.
