2019-2020 Flu Season

Composition of Vaccine

The composition of the U.S. flu vaccines are reviewed annually and updated as needed to match circulating flu viruses.  Flu vaccines protect against three or four viruses (depending on the vaccine) that research suggests will be most common that season.  

Trivalent (three-component) vaccines:

  • H1N1 pdm09-like virus: A/Brisbane/02/2018
  • H3N2-like virus: A/Kansas/14/2017
  • B, Victoria lineage: B/Colorado/06/2017

Quadrivalent vaccines will also include:

  • B, Yamagata lineage: B/Phuket/3073/2013