The Dec. 5 New York Times carries a Page One story explaining the link between cold weather and the flu, but it doesn't explain it quite fully enough. Citing an October study by four microbiologists at New York's Mount Sinai School of Medicine, Times reporter Gina Kolata (author of the strangely gripping Flu: The Story of the Great Influenza Pandemic of 1918 and the Search for the Virus That Caused It) writes that the influenza virus "is more stable and stays in the air longer when air is cold and dry, the exact conditions for much of the flu season." What Kolata breezes past a little too quickly for the lay reader is the relevance of this finding to the warning of mothers down the ages, "You'll catch your death of cold."
On the one hand, these mothers appear to be vindicated in the limited sense that yes, going out into the cold weather increases your risk of catching the flu. (It was long ago established that exposure to cold weather has no effect whatsoever on one's susceptibility to the common cold, which is different from the flu and caused mainly by something called the rhinovirus. Sorry, Mom!) But generations of mothers believed that the flu risk could be averted by wearing a heavy coat, sweater, mittens, scarf, and hat. According to this new study (which, I should point out, involved not humans but guinea pigs), even the most oppressive smothering of children in multiple layers won't protect them against contracting the flu.
This conclusion is of course implied by Kolata's focus on how cold air affects the flu virus, but she addresses the winter-coat question directly only briefly toward the end of her story. "There was no difference in their immune response," she writes, when the guinea pigs were exposed to lower temperatures. Here's how the authors of the Mount Sinai study put it:
innate immunity was not greatly impaired in guinea pigs housed at 5°C relative to those at 20°C. These findings argue against the idea that increased physiological stress experienced under cold conditions leads to a weakening of the immune response.
Translation: If you go outside on a cold day improperly bundled, you'll experience a heightened risk of being cold, but not a heightened risk of getting the flu, relative to others who go outside fully bundled. You will, however, experience a heightened risk of getting the flu relative to others who stay indoors. The best solution for parents is therefore either to imprison their children by keeping them indoors or to move to the tropics, where, Kolata reports, "there is not much flu at all and no real flu season." Or, alternatively—this is what Peter Palese, one of the study's authors, recommends—to get their children a flu shot.