Flu seasons can begin as early as October, and end when the number of positive tests for the virus approaches zero, generally sometime in March or April. There has been a wide variation in the number of deaths attributable to influenza in past seasons — it has reached as high as 49,000 — but the average is around 12,000.

This year’s flu season, however, didn’t officially begin until late last month. And while a true number is difficult to reach — not every sick person is tested, for instance, and the cause of a death in the hospital can be clouded by co-morbidities — it is likely that no more than a few hundred people in America, and possibly far fewer, have died of the flu this winter. Indeed, by any measurement, the statistics are historic and heartening. For every individual who has been hospitalized this season, 22 people were hospitalized in the 2010-11 flu season. Even more strikingly, 122 children died of flu last season and 348 during the flu outbreak of 2009-10 — while this time around that number is 3.

It is hard to overstate the relief that hospitals are experiencing as a result — particularly after the rising prevalence in the last decade of avian and swine flu, which led to fears in both the medical community and the public of a widespread outbreak. As a fellow in infectious diseases at Weill Cornell Medical College told me: “Three years ago I was sitting in an amphitheater being briefed on the influenza pandemic. We were worried we might have to ration ventilators. Now we’ve seen just a handful of cases all winter. I personally haven’t treated a single case of influenza.”

Scientists are still studying the complex relationship between flu and climate, and other factors, like an absence of new strains or immunity from past vaccinations, may have contributed to this season’s low numbers. But there is reason to believe that the weather is an important factor. For one thing, studies have established that the flu virus thrives in low humidity, and therefore low temperature — there’s a reason, after all, that the flu usually hits us in January, not July. Cold weather also dries out the nasal passages, making it easier to get the coughs and sneezes that transmit the flu. And it keeps us cooped up inside, passing illnesses around.