Pasteur Institute specialists warn of pandemic risk of H5N1

Experts at the Pasteur Institute have sounded the alarm over the increasing threat posed by the H5N1 avian influenza virus.

David Corredor

Experts at the Pasteur Institute have sounded the alarm over the increasing threat posed by the H5N1 avian influenza virus. Originally confined to wild birds and poultry, the virus has recently demonstrated the ability to infect mammals, including dairy cattle and even domestic pets. This cross-species transmission raises fears that H5N1 could eventually adapt for efficient human-to-human spread—a scenario that could trigger a pandemic with catastrophic consequences.

Why H5N1 is different?

• Unlike seasonal influenza strains such as H1N1 or H3N2, humans have virtually no immunity to H5 viruses.
• This lack of defense means that if the virus mutates to spread easily among people, the global population would be highly vulnerable.
• Specialists emphasize that influenza pandemics historically occur when a novel strain emerges and spreads rapidly, as seen in 1918, 1957, and 1968.
• H5N1 fits this profile, but with an added danger: its current fatality rate in humans is around 48%, far higher than typical flu strains.

Current human cases and transmission

Human infections remain rare and usually occur through direct contact with infected animals, such as poultry workers or farmers. However, the virus’s ability to infect mammals is a red flag. In recent months, outbreaks in dairy cows in North America and sporadic cases in domestic cats have been documented. The World Health Organization has recorded nearly 1,000 human cases since 2003, underscoring the persistent risk. Alarmingly, the first U.S. case of H5N5—a related strain—was recently confirmed, resulting in a fatal outcome.