Flu Season - From Start to Peak and End

Flu Season Basics

A map showing widespread flu during most of the US during the 2009-10 flu season.
In 2009, there was an early flu season, with widespread flu in most of the country by November. Photo courtesy of the CDC


Although flu season is usually thought of as occurring in the winter, the severity and timing of flu season actually vary from year-to-year.

Flu Season

Flu season is the time of year when you are most likely to get sick from the flu.

In general, flu season can start anytime in late fall, peak in mid-to-late winter (usually January or February), and continue through early spring. On average, flu season lasts about 13 weeks.

  • 2015-16 Flu Season - late start  - 77 pediatric flu deaths.
  • 2014-15 Flu Season - 148 pediatric flu deaths (drifted H3N2 vaccine strain predominate).
  • 2013-14 Flu Season - began increasing in mid-November and peaked in late December  - 111 deaths in children.
  • 2012-13 Flu Season - an early and intense flu season that lasted slightly longer than usual - 171 deaths in what the CDC described as a moderately severe flu season. (H3N2 vaccine strain predominate).
  • 2011-12 Flu Season - was a mild flu season - 37 deaths in children.
  • 2010-11 Flu Season - started in December, peaked in February and ended in April - 123 deaths in children.
  • 2009-10 Flu Season - 2009 H1N1 pandemic flu virus continued from the summer and fall of 2009, peaked in October, and ended in December - 282 deaths in children.
  • 2008-09 Flu Season - seasonal flu season started in December, peaked in February, and ended in April, but then cases of the 2009 H1N1 virus began in May 2009 and continued throughout the summer and fall of 2009 - 133 deaths in children.
  • 2007-08 Flu Season - started in January, peaked in February, and ended in April and was considered to be more severe than the previous three flu seasons - 88 deaths in children (drifted H3N2 vaccine strain predominate).
  • 2006-07 Flu Season - started in December, peaked in February and ended in April - 68 deaths in children.
  • 2005-06 Flu Season - started in February, peaked in March, and ended in April, but was considered a mild flu season - 41 deaths in children.
  • 2004-05 Flu Season - started in December, peaked in February and ended in April - 39 deaths in children.
  • 2003-04 Flu Season - started in October, peaked in November, and ended in December, and was considered to be a moderately severe flu season - 152 deaths in children (H3N2 vaccine strain predominate).

Theories about Flu Season

Why is the flu virus so active in the winter? People used to simply blame the fact that kids are in school and are inside more because of the cold weather, but those were never really satisfying explanations.

Recent research gives an even better explanation - the flu virus is transmitted best at colder temperatures in low humidity, just like we see in the winter.

Flu Season Facts

  • Flu season most commonly peaks in February (50% of the time).
  • In the Southern Hemisphere (Australia, New Zealand, South Africa, etc.), flu season actually occurs in the summer months.
  • You can view past flu season reports at the CDC flu website.

Also Known As: cold and flu season

Alternate Spellings: influenza season

Examples: It is a good idea to get a flu shot before the start of flu season so that you don't get sick with the flu, but even a late flu shot provides protection, especially when flu season lingers into April or May.

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