Researchers at France’s Institut Pasteur have warned that if the H5 strain of bird flu mutates to spread efficiently between humans, it could cause a pandemic more severe than COVID-19. The virus, currently widespread among wild birds, poultry, and some mammals, has disrupted food supplies and killed millions of birds, though human infections remain rare. Marie-Anne Rameix-Welti, medical director at the Pasteur Institute’s Respiratory Infection Center, said the greatest concern is the virus adapting to human-to-human transmission. Since humans lack antibodies against H5, unlike seasonal flu strains H1 and H3, the population would be highly vulnerable. From 2003 to 2025, around 1,000 human infections were recorded, mostly in Egypt, Indonesia, and Vietnam, with a 48% fatality rate. Recent detections in U.S. cattle and the first human H5N5 case in Washington have raised alarms. Experts stress that the pandemic risk remains low but emphasize vigilance and preparedness, noting that vaccine candidates and antivirals are already available.