The Flu Season
In the Northern hemisphere, winter is the time for flu, but the exact timing and duration of flu seasons vary. While flu outbreaks can happen as early as October, most of the time flu activity peaks in January or later.* The figure below shows peak flu activity for the United States by month for the 1976-77 through 2010-11 flu seasons. The “peak month of flu activity” is the month with the highest percentage of respiratory specimens testing positive for influenza virus infection. During this 35-year period, flu activity most often peaked in February (16 seasons, or 46% of the time), followed by January (7 seasons or 20% of the time), and March and December (which each peaked during 4 seasons, or 11% of the time).