Influenza A(H3N2) viruses predominate 2017-2018 season

(HealthDay)—Most influenza viruses identified in the 2017 to 2018 season are influenza A, with A(H3N2) viruses predominating, according to research published in the Feb. 16 issue of the U.S. Centers for Disease Control and Prevention's Morbidity and Mortality Weekly Report.

Alicia P. Budd, M.P.H., from the CDC in Atlanta, and colleagues examined influenza activity in the United States from Oct. 1, 2017, through Feb. 3, 2018. The researchers observed an increase in influenza activity in early November 2017, followed by a sharp increase from December through Feb. 3, 2018. The most commonly identified viruses were influenza A viruses, with A(H3N2) viruses predominating; influenza A(H1N1)pdm09 and influenza B viruses were also reported. A total of 17,101 laboratory-confirmed influenza-related hospitalizations were reported during the study period (cumulative incidence, 59.9 per 100,000 population).

Brendan Flannery, Ph.D., also from the CDC, and colleagues used data from 4,562 children and adults enrolled in the U.S. Influenza Vaccine Effectiveness Network during Nov. 2, 2017, to Feb. 3, 2018. The researchers found that the overall adjusted vaccine effectiveness (VE) against influenza A and influenza B virus infection correlated with medically-attended acute respiratory illness was 36 percent. Sixty-nine percent of influenza infections were caused by A(H3N2) viruses. VE was estimated to be 25, 67, and 42 percent against illness caused by influenza A(H3N2) viruses, A(H1N1)pdm09 viruses, and influenza B viruses, respectively.

"These early VE estimates underscore the need for ongoing influenza prevention and treatment measures," Flannery and colleagues write. "Even with current vaccine effectiveness estimates, vaccination will still prevent influenza illness, including thousands of hospitalizations and deaths."