ON JULY 14TH America’s Centres for Disease Control and Prevention (CDC) reported five new cases of the H5N1 avian flu virus in humans, bringing the total number of cases reported since April to nine. All five were involved in culling infected poultry in Colorado, and appear to have the same strain that has been spreading in dairy cows across the country since December. So far, there is no evidence the virus has adapted to spread between humans, a prerequisite for a flu pandemic. But things can change quickly—the more the virus circulates in animals that come in close contact with humans, the bigger the risk that a pandemic strain will emerge.

Should H5N1 go down this path, would the world be prepared? When SARS-CoV-2 emerged in 2019, humans had no natural immunity, drugs or vaccines. All three exist for H5N1, though how well any of them would work against a possible pandemic virus remains unclear.