Research from the US in ferrets shows that previous infections with seasonal flu viruses or vaccinations might offer some limited protection against the bird flu strain.

Bird flu (H5N1) poses a significant threat due to its high fatality rate in humans and pandemic potential. Understanding whether antibodies generated by common seasonal flu virus strains (H1N1 and H3N2) or their vaccines might offer cross-protection against H5N1 could be crucial for pandemic preparedness.

Previous research from the Johns Hopkins Bloomberg School of Public Health in Baltimore demonstrated that antibodies from healthcare workers recently infected with seasonal flu could recognise bird flu virus strains circulating in dairy cattle. 

Notably, antibodies generated from the seasonal H1N1 infection showed more cross-reactivity to H5N1 than those from H3N2. However, “everybody had relatively low levels of antibodies,” said Andrew Pekosz, group leader at Johns Hopkins, highlighting that, “any boost in antibodies is going to be short lived”.

The same research team has now published a study in Science Translational Medicine that shows that ferrets recently infected with seasonal flu viruses provided some protection against severe illness or death from subsequent exposure to H5N1 and, just as in humans, with effects more relevant in H1N1 than H3N2.

This also provides further evidence for a recent study from Germany which indicated that antibodies targeting neuraminidase (the “N” protein in influenza virus naming) might reduce disease severity, prompting suggestions that future vaccine efforts should focus on this protein rather than hemagglutinin (“H”).

These findings suggest limited and transient cross-protection between seasonal influenza antibodies and H5N1 but will become crucial to evaluate the actual protective potential of flu antibodies in human infections and vaccination research and strategies.