Influenza cases breach baseline threshold for first time this season

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Takeaway

  • Influenza-like illness (ILI) exceeded the national baseline level for the first time this influenza season, increasing to 2.3% during the week of December 17.

Why this matters

  • This season’s trivalent and quadrivalent influenza vaccine formulations are well-matched to almost all currently circulating influenza viruses, which are also sensitive to the antivirals oseltamivir, zanamivir, and peramivir.

Study design

  • US Centers for Disease Control and Prevention (CDC) Morbidity and Mortality Weekly Report (MMWR) update on influenza activity from October to mid-December 2016.

Key results

  • After a steady increase in activity during November and early December, outpatient visits for ILI exceeded the national baseline level of 2.2% for the first time this season. 
  • Levels increased from 1.9% during the week of December 10 to 2.3% during the week of December 17.
  • Influenza A viruses were identified most frequently, with influenza A (H3N2) viruses predominating. 
  • Almost all viruses characterized thus far this season have been similar to the components of the 2016-17 Northern Hemisphere trivalent and quadrivalent influenza vaccine formulations.
  • All influenza viruses tested to date have been sensitive to the antiviral drugs oseltamivir, zanamivir, and peramivir.