💉 Strengthening our immunity against the risk of avian flu

A team from UNIGE shows that some seasonal flu antibodies also attack avian flu. Stimulating them would strengthen our protection in case of a pandemic.

Are seasonal flu antibodies also effective against avian flu? A team from the University of Geneva (UNIGE) shows that a specific type of antibody linked to the first virus, already present in the entire population, could provide basic protection against the second. However, this protection varies depending on age and vaccination history. Published in Nature Communications, these results provide key elements for anticipating a potential avian flu pandemic.


Circulating in many regions of the world - including Switzerland - the avian influenza A H5N1 virus spreads mainly among birds. However, several transmissions to cattle, and then to humans, have recently been observed in North America (71 cases reported in the United States), reigniting concerns about the risk of a future pandemic. A variant from a specific evolutionary lineage of the virus - clade 2.3.4.4b - is of particular interest to epidemiologists due to its virulence.

Several studies have shown that pre-existing immunity against human seasonal flu viruses could modulate the severity of an H5N1 infection. "We have all been exposed to these viruses and therefore possess antibodies directed against them, which share a common genetic basis with H5N1. Some of these antibodies - so-called cross-reactive ones - are thus capable of recognizing H5N1 and, to some extent, fighting it," explains Benjamin Meyer, a scientific collaborator at the Center for Vaccinology in the Department of Pathology and Immunology of the UNIGE Faculty of Medicine.

People vaccinated in 2009 during the H1N1 flu pandemic today have higher concentrations of cross-reactive antibodies.

Vaccinated in 2009? More antibodies

Thanks to recent work, Benjamin Meyer and his team have highlighted that these cross-reactive antibodies primarily attack the virus's "stalk," which it has in common with seasonal flu, and not its "head," which changes frequently. But most importantly, the scientists discovered that these antibodies, unlike others, do not prevent the H5N1 virus from entering cells, but block its ability to spread from one cell to another.

Indeed, once replicated within its host, the virus exits but remains attached to the cell membrane. To detach itself and continue its infection, it uses a protein acting as molecular scissors. It is this "cutting" process that the cross-reactive antibodies inhibit, with varying effectiveness among individuals.

By examining these individual differences, the scientists revealed another important result: people vaccinated in 2009 during the H1N1 flu pandemic — with a vaccine containing an adjuvant designed to amplify the immune response — today have higher concentrations of cross-reactive antibodies, capable of effectively neutralizing the H5N1 virus. In people who received a standard seasonal flu vaccine, no increase in cross-reactive antibodies was detected. The enhanced immune response could be associated with less severe symptoms in case of avian flu infection.

Year of birth also important

"Our study also shows that early life exposure plays an important role: people born before 1965 — who were exposed during childhood to seasonal flu viruses of the H1 or H2 subtypes — naturally have higher levels of antibodies against H5N1. Conversely, those born later were exposed to other subtypes of seasonal flu and have a lower level of basic protection," says Mariana Alcocer Bonifaz, a researcher at the Center for Vaccinology in the Department of Pathology and Immunology of the UNIGE Faculty of Medicine, and first author of this publication.

These results highlight the importance of vaccination with adjuvant against seasonal flu to broaden the immune response against the risk of an avian flu pandemic. Such a strategy would also present a major advantage in case of a pandemic: the amount of H5N1 vaccine — already available — needed per person would be much lower compared to flu vaccination without adjuvant, which would increase the overall vaccination capacity for the same production level.