Designing a reoriented H5 hemagglutinin to generate stem-directed, heterosubtypic immunity to influenza A viruses

A reoriented H5 hemagglutinin vaccine, reoH5HAPhe (A/Vietnam/1203/2004), elicited stem-directed antibodies that protected naive mice from heterologous H5N1 lethal challenge.

• Why it matters: Seasonal influenza vaccines offer limited cross-protection, and antibody responses to conventional candidates focus on the variable HA head rather than the conserved stem.
• What they did: Mice received a single alum-adjuvanted immunization with reoH5HAPhe or were boosted after seasonal vaccination; protection was tested against heterologous H5N1 (A/Texas/37/2024) and heterosubtypic H1N1 challenge, with electron microscopy polyclonal epitope mapping.
• The result: reoH5HAPhe protected naive mice against lethal H5N1 challenge, and boosting conferred complete heterologous protection in seasonally pre-immunized mice; stem-directed responses also protected against H1N1, reducing viral replication and improving survival despite limited cross-neutralizing activity.