The bird flu outbreak among dairy cows continues to generate alarm, despite reassuring news that pasteurised milk is unlikely to infect anyone with H5N1. Scientists cannot stop worrying about a nightmare scenario: that the virus will get into pigs and, from there, spark a human pandemic.

Pigs “are the perfect vessels through which an even more virulent strain could emerge,” said Dr Nirav Shah, principal deputy director of the Centres for Disease Control and Prevention, at a May 2 briefing by the Council on Foreign Relations.