In comparison to the last three seasons, the 2010-2011 influenza season was less severe than both the pandemic year (2009-2010) and the 2007-2008 season, but more severe than the 2008-2009 influenza season, as determined by the percentage of deaths resulting from pneumonia or influenza, the number of influenza-associated pediatric deaths reported, adult and pediatric hospitalization rates, and the percentage of visits to outpatient clinics for influenza-like illness (ILI).
Overall, during the 2010-2011 influenza season, the most commonly reported viruses were influenza A (H3N2), but 2009 influenza A (H1N1) viruses and influenza B viruses circulated as well. Because a certain age group may be hit harder by one type of influenza virus than another (for example, the 2009 H1N1 virus has disproportionately affected people younger than 65 years of age than those older than 65 whereas H3N2 virus often affects those older than 65 years), the 2010-2011 influenza season had a substantial health effect on every age group.
Flu seasons are unpredictable in a number of ways, including when they begin, how severe they are, how long they last, which viruses will spread, and whether the viruses in the vaccine match flu viruses that are circulating.
Additional information about flu activity during the 2010-2011 season can be found in the MMWR article Update: Influenza Activity – United States, 2010-11 Season, and Composition of the 2011-12 Influenza Vaccine.
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