Flu Season—Is It Over Yet?
Some of you have been wondering when flu season occurs. Or maybe I should say, you’re wondering when it will end. The good news is, it’s finally winding down for this year. That’s because the flu follows a distinctly seasonal pattern. In the Northern Hemisphere, the season begins in late fall, peaks in mid-winter, and diminishes again in early spring. By late spring through late summer, influenza is extremely uncommon. Essentially, flu season is over, for now.
But that doesn’t mean the influenza virus has disappeared. Scientists believe that it remains at large in the population, biding its time until the following winter, to strike again in epidemic fashion. This curious pattern, linking the seasons with the incidence of flu and other respiratory viruses, has led many scientists to speculate about the seasonal nature of influenza.
Recent research suggests that several aspects of winter weather may conspire to encourage flu outbreaks. These viruses seem to thrive in cold weather, for instance. Cold temperatures cause them to alter their structures somewhat, which may affect their infectivity. And the lack of sunshine in winter is linked to reduced vitamin D levels in the population, which may also influence how susceptible people are to infection. Relative humidity is another factor that may play a role in the seasonality of flu and other respiratory viruses, such as respiratory syncytial virus (RSV), which disproportionately affects young children.
In fact, the very term “cold” hints at the fact that the common cold is linked to cold weather. While its certainly possible to get a cold at any time of the year, they’re more common in winter, much like the flu and RSV. Unfortunately, cold season tends to peak in early spring in the United States. But the end is in sight.
To summarize, research shows that two common winter conditions encourage respiratory viruses: cold temperatures and dry air. As with the common cold, one of your best lines of defense is rigorous hand washing to remove viruses from your hands before they’re transmitted to your eyes, nose, or mouth.
du Prel JB1, Puppe W, Gröndahl B, Knuf M, Weigl JA, Schaaff F, Schmitt HJ.Are meteorological parameters associated with acute respiratory tract infections?Clin Infect Dis. 2009 Sep 15;49(6):861-8. doi: 10.1086/605435.