Two clinical trials of the vaccine likely to be used, under way since last year, have yet to produce data.

If the virus currently causing an outbreak of avian influenza among U.S. dairy cattle were to begin spreading widely among humans, the federal government says it could distribute enough vaccines within four months to inoculate a fifth of the U.S. population.

If the virus currently causing an outbreak of avian influenza among U.S. dairy cattle were to begin spreading widely among humans, the federal government says it could distribute enough vaccines within four months to inoculate a fifth of the U.S. population.
How effective that vaccine would be, and whether those doses would do enough to blunt the impact of a human pandemic, isn’t clear. Two clinical trials of the vaccine likely to be used, under way since last year, have yet to produce data.

The strain of avian flu known as H5N1 has been circulating among birds in the U.S. since late 2021, and is known only to have infected two people in the country, including a Texas dairy worker last month. U.S. officials aren’t near pulling the trigger on plans to roll out emergency vaccinations.