People may have preexisting immunity to bird flu

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How immune are people to bird flu viruses? To find out, Canadian virologists analyzed blood samples that 24 health care workers at Université de Montréal's teaching hospital, the CHUM, gave before and after getting their annual flu shot.

They then assessed the ability of antibodies in that blood to recognize various strains of influenza virus, including several of the highly contagious and widespread H5 variety found in North America and Asia.

The result? Before vaccination, most participants already had antibodies against the viruses, the researchers found. In some cases, these antibodies were able to neutralize the viruses and eliminate cells displaying viral proteins on their surface.

The finding is published this month in the Journal of Virology.

"Raises important questions"

"What particularly surprised us was that in several participants this cross-reactivity was already present before vaccination," said the study's first author, Katrina Dionne, a UdeM doctoral student supervised by UdeM immunologist Andrés Finzi.

"This raises important questions about how our previous exposure to influenza viruses may influence our response to new avian influenza viruses," said Dionne.

Preexisting immunity may result from previous exposure to different influenza viruses or from vaccinations received over the years, Dionne and Finzi believe, suggesting that each person's immune history helps shape their ability to recognize new related viruses.

Some caution advised

The study also shows that, in some people, seasonal vaccination against the H1N1 and H3N2 strains induces antibodies that are capable of recognizing H5Nx viruses. However, the researchers did not observe a marked increase in this cross-reactivity following vaccination.

Hence it's unclear whether the seasonal flu shot protects against H5N1 or other emerging avian influenza viruses, the researchers say. So it's important that vaccines be developed that specifically target these viruses when future outbreaks occur, they add.

"This study gives us a better understanding of the extent of immunity already present in the population against certain avian influenza viruses," said Finzi, a researcher in the immunopathology research lab of the CHUM's research center, the CRCHUM.

"This knowledge could contribute to the development of vaccination strategies offering broader protection against future emerging influenza viruses," he said.

Publication details

Katrina Dionne et al., Pre-existing cross-subtype serological responses against H5Nx in health care workers, Journal of Virology (2026). DOI: 10.1128/jvi.01310-26

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Citation: People may have preexisting immunity to bird flu (2026, October 26) retrieved 26 October 2026 from https://phys.org/news/2026-10-people-preexisting-immunity-bird-flu.html

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