The convergence of multiple flu strains in one animal can allow new virus strains to form—just as they did in past pandemics.

With the approach of fall and cooler weather across the United States, officials say the risk posed by the H5N1 bird flu virus could rise — and they’re taking steps to prevent the creation of a hybrid flu virus that could more easily infect humans.

The world is watching how the U.S. is responding to the H5N1 bird flu outbreak in dairy cattle, a top WHO official said.