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CDC: H3N2 dominates 2014-2015 flu season
Influenza A (H3N2) viruses were prevalent during the 2014-2015 season, with influenza B viruses becoming more common later in the season, according to data recently published in MMWR.
“The 2014-2015 influenza season was moderately severe overall ... with predominant circulation of antigenically and genetically drifted influenza A (H3N2) viruses,” the researchers wrote. “Influenza activity this season was similar to the 2012-2013 season, which was the most recent influenza A (H3N2)-predominant season, but with higher rates of influenza-associated hospitalizations among adults aged [65 years or older.]”
From Sept. 28 to May 23, there were 691,952 specimens tested for influenza. Of the 125,462 which tested positive, influenza A viruses comprised 83.5% of confirmed specimens, which were predominantly of the H3N2 subtype (99.6%).
Influenza activity peaked during late December and early January; however, a growing prevalence of influenza B activity was observed from late February through the middle of May.
“Influenza vaccination this season offered reduced protection against the predominant circulating viruses, drifted influenza A (H3N2), compared with previous seasons when most circulating and vaccine strain viruses were well-matched,” the researchers wrote. “Influenza vaccination provided protection against vaccine-like influenza A (H3N2) viruses that had not undergone significant antigenic drift and against influenza B viruses, which predominated later in the season.”
There were 17,911 hospitalizations resulting from influenza between Oct. 1 and April 30. Approximately 61% of hospitalizations were among adults aged 65 years or older, the age group with the highest rate of influenza incidence.
As of May 23, there were 141 lab-confirmed cases of influenza-associated pediatric deaths. Of these, 109 were associated with influenza A virus, 29 with influenza B virus, and one with influenza A and influenza B coinfection.
According to the researchers, the FDA’s Vaccines and Related Biological Products Advisory Committee recommended the 2015-2016 trivalent influenza vaccine contain A/California/7/2009 (H1N1)pdm09-like virus, A/Switzerland/9715293/2013 (H3N2)-like virus and B/Phuket/3073/2013-like (B/Yamagata lineage) virus. Quadrivalent vaccines should also include B/Brisbane/60/2008-like (B/Victoria lineage) virus. This decision was made after consideration of global virologic and epidemiologic surveillance, genetic characterization, antigenic characterization, antiviral resistance and candidate vaccine viruses available for mass-production. – by Dave Muoio
Disclosure: The researchers report no relevant financial disclosures