Although summer is just beginning, the U.S. Food and Drug Administration has already announced the components of the influenza vaccine for the northern hemisphere in the 2017-2018 flu season.

For the trivalent vaccine the components are:

  • A/Michigan/45/2015 (H1N1)pdm09-like virus
  • A/Hong  Kong/4801/2014 (H3N2)-like virus
  • B/Brisbane/60/2008-like virus (B/Victoria lineage)

 In addition to the above, the quadrivalent vaccine will contain:

  • B/Phuket/3073/2013-like virus (B/Yamagata)

So how are flu vaccine components determined? There are more than 100 national influenza centers located throughout the world. These centers conduct year-round surveillance for influenza, involving testing thousands of influenza virus samples from patients. From these samples, the centers send representative viruses to five World Health Organization (WHO) Collaborating Centers for Reference and Research on Influenza, which are located in Atlanta, Georgia,United States; London, United Kingdom; Melbourne, Australia; Tokyo, Japan; and Beijing, China. As one of these Collaborating Centers, the Centers for Disease Control and Prevention (CDC) in Atlanta receives and tests thousands of influenza viruses from around the world.

Twice a year, the WHO consults with the directors of the WHO Collaborating Centers and with representatives of key national laboratories and academies. At these meetings, which take place in February for the selection of the upcoming northern hemisphere’s seasonal influenza vaccine and in September for the southern hemisphere’s vaccine, the WHO recommends specific vaccine viruses for inclusion in the vaccines.  Based on the WHO recommendations, each country then makes their own decision about which viruses should be included in influenza vaccines to be licensed in their country.

In the United States, the FDA makes the final decision about vaccine viruses to be included in flu vaccines to be sold. As soon as a decision has been made concerning which viruses should be incorporated into the vaccine, private sector manufacturers begin the process of producing the vaccine. The manufacturing process is time sensitive, as it takes at least six months to produce large quantities of influenza vaccine.  In order for vaccines to be delivered in time for vaccination to begin in the fall, manufacturers may actually begin to grow one or more of the vaccine viruses as early as January, based on their best guess as to what viruses are most likely to be included in the vaccine.

What Is The Best Time To Get A Flu Shot?

In western Pennsylvania, the flu season generally occurs in mid/late October through March. Since it takes approximately two weeks for protective vaccine antibodies to develop, September and early October are considered to be optimal times to receive a flu shot. However, a flu shot may be received at any time, even when the flu illness has actually occurred in the community.

What Is The Best Flu Vaccine Formulation To Receive—Trivalent or Quadrivalent?

In addition to the trivalent and quadrivalent formulations, in recent years a “high dose” flu vaccine has been developed specifically for people 65 years of age and older.

Keep in mind that, as with any health-related issue, it is best to discuss flu immunization with your doctor in making the decision as to which flu vaccine is most suitable for you. For additional information, visit