CDC: pH1N1 dominated 2013-2014 influenza season

Influenza activity peaked in late December during the 2013-2014 season and influenza A (H1N1)pdm09 viruses predominated, according to CDC data published in MMWR.

In week 13, the week ending March 29, influenza B viruses became the most common influenza virus in circulation.

“This influenza season was the first since the 2009 pH1N1 pandemic in which pH1N1 viruses predominated and was characterized overall by lower levels of outpatient illness and mortality than influenza A(H3N2)–predominant seasons, but higher rates of hospitalization among adults aged 50-64 years compared with recent years,” CDC researchers wrote.

From Sept. 29 to May 17, there were 308,741 specimens tested for influenza, and 53,470 (17.3%) were positive. The majority (87.4%) were influenza A viruses, and 67.1% of those (n=31,353) were subtyped. Among those, 90.3% were pH1N1 viruses. There was one case of a variant H3N2 virus during week 30, the week ending Oct. 5.

There were 9,635 reported influenza hospitalizations during the season. Adults aged 18 to 64 years accounted for 57.4% of the hospitalization. Among patients with medical chart data available, 89% of the hospitalized patients had at least one underlying medical condition. The most frequent conditions were obesity, metabolic disorders and cardiovascular disease.

According to the report, the FDA’s Vaccines and Related Biological Products Advisory Committee has determined that the 2014-2015 influenza vaccines will have the same composition as the 2013-2014 vaccine. The trivalent vaccine should contain A/California/7/2009-like virus (pH1N1), A/Texas/50-2012-like virus (H3N2) and a B/Massachusetts/2/2012-like virus (B/Yamagata lineage). Quadrivalent vaccines will also include a B/Brisbane/60/2008-like virus (B/Victoria lineage).

Disclosure: The researchers report no relevant financial disclosures.