The bird flu virus that has been spreading among wild birds, poultry and mammals could lead to a pandemic worse than Covid-19 if it mutates to transmit between humans, the head of France's Institut Pasteur respiratory infections center has said. "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," Marie-Anne Rameix-Welti told Reuters.