Influenza A(H1N1)pdm09, influenza A(H3N2) and influenza B viruses circulated worldwide from May 18 to Sept. 20, but the United States experienced low levels of influenza activity, according to the CDC.
“It is not possible to predict which influenza virus will predominate or how severe influenza-related disease activity will be during the 2014-2015 influenza season,” researchers with the influenza division in CDC’s National Center for Immunization and Respiratory Diseases, wrote in MMWR. “Annual influenza vaccination is the best method for preventing influenza and its potentially severe complications.”
In the United States, WHO collaborating laboratories and the National Respiratory and Enteric Virus Surveillance System tested 66,006 specimens during the time period and 3,209 (4.9%) were positive for influenza. Fifty-four percent of those were influenza A viruses. Among the 1,728 influenza A viruses, 64% were subtyped and 96% were influenza A(H3N2) viruses. There were two cases of H3N2 variant viruses in Ohio among two patients who reported direct contact with swine.
Influenza was reported in 47 states and the District of Columbia, Guam and Puerto Rico.
The percentage of outpatient visits for ILI ranged from 0.8% to 1.4% and was below the national baseline of 2%. The percentage of deaths attributed to pneumonia and influenza ranged from 5.2% to 6% and was below the epidemic threshold. There were five influenza-associated pediatric deaths.
Worldwide, countries in the temperate climate Southern Hemisphere experienced typical seasonal influenza. Influenza A viruses predominated in Australia and New Zealand, though pH1N1 viruses were more frequent than H3N2 viruses. In South America, influenza A viruses also were more common, with H3N2 viruses predominating in Chile, Argentina, Uruguay and Paraguay. Influenza A viruses also predominated in tropical South America and in South Asia and Southeast Asia.
The recommended components for the 2014-2015 influenza vaccine in the Northern Hemisphere are A/California/7/2009 (H1N1)-like virus, A/Texas/50/202 (H3N2)-like virus and B/Massachusetts/2/2012-like (B/Yamagata lineage) virus. The quadrivalent vaccine also will include B/Brisbane/60/2008-like (B/Victoria lineage) virus.
The CDC recommends that all persons aged 6 months and older receive an influenza vaccine. For the 2014-2015 season, the projected vaccine supply is 151 million to 159 million doses.
“Vaccination is the first line of defense against influenza,” the researchers wrote. “Even during seasons when the match between the vaccine viruses and circulating viruses is less than optimal and protection against illness might be reduced, vaccination can offer substantial benefit and might reduce the likelihood of severe outcomes such as hospitalization and death.”
Disclosures: The researchers report no relevant financial disclosures.