Influenza Activity Increasing in United States

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Currently circulating viruses seem not to have undergone significant antigenic drift.
Currently circulating viruses seem not to have undergone significant antigenic drift.

HealthDay News — Influenza activity was low during October 2017 but started increasing in November, with influenza A, predominantly A(H3N2), most commonly identified, according to research published in the US Centers for Disease Control and Prevention's Morbidity and Mortality Weekly Report.

Vivien G. Dugan, PhD, from the CDC in Atlanta, and colleagues summarized US influenza activity during October 1 to November 25, 2017.

The researchers note that influenza activity was low during October 2017 in the United States, but since the start of November, activity has been increasing. The most commonly identified viruses have been influenza A viruses, with influenza A(H3N2) predominating. 

Several indicators of influenza activity were reported to be higher than normally seen at this time of year. Most influenza viruses characterized during this period were genetically or antigenically similar to the Northern Hemisphere cell-grown vaccine reference viruses for 2017 to 2018. Currently circulating viruses seem not to have undergone significant antigenic drift; circulating A(H3N2) viruses are antigenically less similar to egg-grown A(H3N2) viruses used for most US influenza vaccine production. Hospitalizations and deaths were more common and vaccine effectiveness was lower in recent past seasons in which A(H3N2) viruses predominated; it is unclear which influenza viruses will predominate in the 2017 to 2018 season.

"Vaccination should continue to be offered as long as influenza viruses are circulating and unexpired vaccine is available," the authors write.

One author disclosed holding two patents relating to influenza vaccines.

Reference

Dugan VG, Blanton L, Elal AIA,et al. Update: influenza activity- United States, October 1- November 25, 2017. MMWR Morb Mortal Wkly Rep. 2017;66(48):1318-1326.



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