The US is entering a riskier season for spread of H5N1 bird flu. Here’s why experts are worriedThe US is entering a riskier season for spread of H5N1 bird flu. Here’s why experts are worried 

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.