Bird flu virus could trigger pandemic worse than Covid, French expert says

French health experts are warning that the highly pathogenic H5 strain of bird flu, already devastating wild and farm animals, could evolve into a virus capable of human-to-human transmission — potentially sparking a pandemic worse than COVID-19.

For the past two and a half years, researchers have observed intense circulation of H5 influenza among wild birds, with outbreaks spilling into domestic poultry and even mammals.

“Because of this intense circulation, we’re seeing a proliferation of outbreaks in farm animals, especially domestic poultry, and an increase in cases of infection in various mammals,” said Marie-Anne Rameix-Welti, Medical Director at the Institut Pasteur’s Respiratory Infections Centre.

“In this context, with the increasing number of infected animals, including those in contact with humans, we fear a rise in human transmission.”

A recent outbreak in eastern France has killed thousands of migratory cranes since October 20, prompting emergency measures and large-scale culling. Human infections remain rare, but the spread to mammals raises alarm among health authorities.

Human cases already detected worldwide

Rameix-Welti confirmed that the transmission of the H5 virus to humans is possible. “Over the last two years, we’ve had more than 70 cases in the Americas, and we also have cases in Southeast Asia, notably in Cambodia and Bangladesh,” she said.

These infections have so far been zoonotic, that is transmitted from animals to humans without evidence of human-to-human spread.

“What we fear,” she warned, “is the virus adapting to mammals, particularly to humans, and becoming capable of human-to-human transmission. That virus would be a pandemic virus. And that’s what we fear most.”

The World Health Organization (WHO) reports nearly 1,000 human infections with avian influenza since 2003 — mostly in Egypt, Indonesia, and Vietnam — with a fatality rate of around 48%.

Meanwhile, the United States confirmed the first human case of the H5N5 strain earlier this month in Washington state; the patient, who had underlying conditions, later died.

“Potentially more severe than COVID-19”

Rameix-Welti cautioned that if the virus adapted to humans, it could cause a pandemic even more severe than COVID-19. “We would find ourselves in the same situation — with a virus against which the human population has absolutely no immunity,” she said. “Flu viruses can be highly virulent; even seasonal flu remains dangerous for vulnerable people, and sometimes for healthy individuals without any particular risk factors.”

Unlike COVID-19, influenza viruses can infect a broader range of species, allowing them to evolve more rapidly. This adaptability makes close monitoring critical.

Scientists say the world is better prepared

Despite the warnings, experts highlight one crucial advantage. “The positive point with the flu, compared to COVID, is that we already have specific preventative measures in place,” Rameix-Welti explained. “We have vaccine candidates ready and know how to manufacture them quickly. And we also have stockpiles of antivirals that, in principle, would be effective against this avian influenza virus.”

The Institut Pasteur, one of Europe’s leading research centres, played a pivotal role during the early days of COVID-19, developing and sharing detection tests worldwide through the World Health Organization. The institute is now among those closely tracking the evolution of the H5 virus and testing vaccine prototypes.

Health authorities remain on high alert as outbreaks continue to affect bird populations across continents. While human infections remain isolated, scientists warn that each new spillover increases the risk of a viral mutation with pandemic potential.

As Rameix-Welti put it: “We’re not facing a crisis yet but the conditions for one are already here. The more the virus spreads among animals, the closer we get to the moment it might cross the line into sustained human transmission.”

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