CDC: Severity of Influenza Season Low Through Feb. 2, 2019

Vaccine effectiveness 47 percent against all flu virus infection associated with acute respiratory illness

THURSDAY, Feb. 14, 2019 (HealthDay News) -- The 2018 to 2019 influenza season has been low in severity so far, and overall vaccine effectiveness is about 47 percent, according to two reports published in the Feb. 15 issue of the U.S. Centers for Disease Control and Prevention Morbidity and Mortality Weekly Report.

Lenee Blanton, M.P.H., from the CDC in Atlanta, and colleagues collected, compiled, and analyzed data to provide an update on influenza activity and viruses in the United States. The researchers note that influenza activity was low during October and November of 2018, increased in late December 2018, and remained elevated through early February 2019. The season was considered to be low-severity as of Feb. 2, 2019; compared with recent seasons, there have been a lower percentage of outpatient visits for influenza-like illness, lower rates of hospitalization, and fewer deaths due to pneumonia and influenza. Influenza A(H1N1)pdm09 viruses predominated in most areas of the country.

Joshua D. Doyle, M.D., Ph.D., also from the CDC, and colleagues used data from 3,254 children and adults enrolled in the U.S. Influenza Vaccine Effectiveness Network during Nov. 23, 2018, to Feb. 2, 2019, to examine vaccine effectiveness. The researchers found that overall adjusted vaccine effectiveness against all influenza virus infection associated with medically attended acute respiratory illness was 47 percent during this period. The overall vaccine effectiveness was 61 percent among children aged 6 months to 17 years. Against illness caused by influenza A(H1N1)pdm09 viruses, vaccine effectiveness was estimated to be 46 percent.

"CDC will continue to monitor influenza disease throughout the season to better understand the impact of vaccination, identify factors associated with reduced protection, and support efforts to improve influenza vaccine," Doyle and colleagues write.

Several authors from the Doyle study disclosed financial ties to the pharmaceutical industry.

Abstract/Full Text - Blanton
Abstract/Full Text - Doyle

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