Bird Flu Mutation Could Trigger Severe Pandemic, Institut Pasteur Warns

Bird Flu Mutation among wild birds, poultry, and several mammal species could spark a pandemic more severe than COVID-19 if it mutates to spread between humans, France’s Institut Pasteur said on Nov. 27 in Paris. Health experts said the risk remains low but urged readiness in case the virus adapts.

Rising concerns over mutation risk

Marie-Anne Rameix-Welti, medical director at the Institut Pasteur’s respiratory infections centre, said the concern centers on the H5 strain’s ability to adapt. The Bird Flu Mutation is already highly pathogenic in birds and has caused the culling of hundreds of millions of animals in recent years. The outbreaks have disrupted food supplies and contributed to higher prices in several regions.

“What we fear is the virus adapting to mammals, and particularly to humans, becoming capable of human-to-human transmission, and that virus would be a pandemic virus,” Rameix-Welti said, noting that a Bird Flu Mutation could accelerate such adaptation. She noted that human cases have occurred but are rare and typically linked to close contact with infected animals.

The Institut Pasteur was one of the first European laboratories to develop and share COVID-19 detection tests in early 2020, helping expand global diagnostic capacity.

Limited immunity and higher potential impact of Bird Flu Mutation

People lack antibodies against H5 bird flu, Rameix-Welti said. Most individuals have immunity from exposure to seasonal flu strains such as H1 and H3, but that protection does not extend to the H5 subtype now affecting birds and some mammals. She said the situation mirrors the early days of COVID-19, when populations had no baseline protection, and warned that a Bird Flu Mutation could further reduce defenses.

Immunity gaps pose challenge

Unlike COVID-19, which largely causes severe illness in older adults or those with underlying conditions, flu viruses can also lead to fatal infections in healthy individuals, including children. “A bird flu pandemic would probably be quite severe, potentially even more severe than the pandemic we experienced,” Rameix-Welti said.

Human infections with H5 viruses have been reported for years, including cases linked to the H5N1 strain circulating among poultry and dairy cows in the U.S. A first human case of H5N5 was confirmed this month in Washington state. The infected man, who had underlying conditions, died last week. According to the World Health Organization, nearly 1,000 human cases of bird flu were documented between 2003 and 2025, mainly in Egypt, Indonesia and Vietnam, with a fatality rate of 48%. Experts noted that a dangerous Bird Flu Mutation spreading in mammals would dramatically increase risk.

Preparedness measures provide advantage

Despite the potential severity, health authorities said the probability of a large-scale human outbreak remains low. Gregorio Torres, head of the Science Department at the World Organisation for Animal Health, said there is no evidence of sustained human-to-human transmission.

“We need to be prepared to respond early enough. But for the time being, you can happily walk in the forest, eat chicken and eggs and enjoy your life. Pandemic risk is a possibility. But in terms of probability, it’s still very low,” Torres said.

Global readiness improving

Rameix-Welti said global preparedness has improved since the COVID-19 pandemic. “The positive point with flu, compared to COVID, is we have specific preventative measures in place. We have vaccine candidates ready and know how to manufacture a vaccine quickly,” she said.

She added that countries also maintain antiviral stockpiles that could be effective if the virus or mutates. These treatments, combined with earlier surveillance and rapid response systems, could help limit the spread of a future outbreak.

Health authorities continue to monitor cases in birds, livestock, and humans, focusing on early detection of any signs that the virus is adapting for efficient human transmission.