From November through December 2013, CDC has received a number of reports from several states of severe respiratory illness among young and middle-aged adults, many of whom were infected with influenza A (H1N1) pdm09 (pH1N1) virus. Multiple pH1N1-associated hospitalizations, including many requiring intensive care unit (ICU) admission, and some fatalities have been reported. The pH1N1 virus that emerged in 2009 caused more illness in children and young adults, compared to older adults, although severe illness was seen in all age groups. While it is not possible to predict which influenza viruses will predominate during the entire 2013-14 influenza season, pH1N1 has been the predominant circulating virus so far. For the 2013-14 season, if pH1N1 virus continues to circulate widely, illness that disproportionately affects young and middle-aged adults may occur.
Recommendations for Healthcare Providers
Clinicians should encourage all patients 6 months of age and older who have not yet received an influenza vaccine this season to be vaccinated against influenza. There are several flu vaccine options for the 2013-2014 flu season and all available vaccine formulations this season contain a pH1N1 component; CDC does not recommend one flu vaccine formulation over another.
Clinicians should encourage all persons of all ages with influenza-like illness who are at high risk for influenza complications (see list at http://www.bt.cdc.gov/HAN/han00359.asp
) to seek care promptly to determine if treatment with influenza antiviral medications is warranted.