When bird flu first struck dairy cattle a year ago, it seemed possible that it might affect a few isolated herds and disappear as quickly as it had appeared.

Instead, the virus has infected more than 900 herds and dozens of people, killing one, and the outbreak shows no signs of abating.

A human pandemic is not inevitable, even now, more than a dozen experts said in interviews. But a series of developments over the past few weeks indicates that the possibility is no longer remote.

Toothless guidelines, inadequate testing and long delays in releasing data — echoes of the missteps during the Covid-19 pandemic — have squandered opportunities for containing the outbreak, the experts said.

In one example emblematic of the disarray, a few dairy herds in Idaho that were infected with bird flu in the spring displayed mild symptoms for a second time in the late fall, The New York Times has learned.

In mid-January, the Department of Agriculture said that no new infections in Idaho herds had been identified since October. But state officials publicly discussed milder cases in November.