Since the start of the bird flu outbreak in U.S. cattle more than eight months ago, health authorities have reported 57 human cases of H5N1 viral infections, a startling number in a country that had previously reported only one. All, though, have been mild.

The fact that none has been severe has been a shock, though a welcome one, certainly. For more than two decades, H5N1 — which has been confirmed in nearly 1,000 people, largely in Asia and Egypt — has had a well-earned reputation as a very dangerous pathogen, with a case fatality rate in the 50% range, putting it in line with Ebola viruses.

To try to get a better handle on the issues that the scientific community does think could be at play, STAT picked the brains of 21 researchers who have studied aspects of influenza — and this specific virus — for years. We posed a series of questions to them, sometimes in interviews, other times in writing.

The answers — which we have categorized in a series of hypotheses below — are illuminating in that they shed light on how a flummoxed field is trying to grapple with facts that challenge the accepted wisdom about a virus that has worried flu scientists since its first foray into humans in 1997.    READ MORE