Ask Dr. Pat · Health

Influenza 2016: Do I Really Need to Get a Flu Shot?

Why Get Vaccinated?

An annual seasonal flu vaccine is the best way to reduce the chances that you will get seasonal flu and spread it to others. When more people get vaccinated against the flu, less flu can spread through that community. Flu vaccines cause antibodies to develop in the body about two weeks after vaccination. These antibodies provide protection against infection with the viruses that are in the vaccine. The seasonal flu vaccine protects against the influenza viruses that research indicates will be most common during the upcoming season. Traditional flu vaccines (called “trivalent” vaccines) are made to protect against three flu viruses; an influenza A (H1N1) virus, an influenza A (H3N2) virus, and an influenza B virus. There are also flu vaccines made to protect against four flu viruses (called “quadrivalent” vaccines). These vaccines protect against the same viruses as the trivalent vaccine and an additional B virus. Effective measures against influenza A and B diseases include prevention of infection by either vaccination with inactivated or live attenuated vaccines. Studies of healthy young adults have shown influenza vaccine to be 70 percent to 90 percent effective in preventing influenza A illness, with moderately lower efficacy rates in the elderly. A flu vaccine is needed every season for two reasons. First, the body’s immune response from vaccination declines over time, so an annual vaccine is needed for optimal protection. Second, because flu viruses are constantly changing, the formulation of the flu vaccine is reviewed each year and sometimes updated to keep up with changing flu viruses. For the best protection, everyone 6 months and older should get vaccinated annually.

What are the main factors that influence which viruses are selected for use in influenza vaccine production?

The isolation of the influenza virus 80 years ago in 1933 very quickly led to the development of the first generation of live-attenuated vaccines. The first inactivated influenza vaccine was monovalent , that is only one strain of the Influenza virus: Influenza A. In 1942, a bivalent vaccine (both Influenza A and B) was produced after the discovery of influenza B. It was later discovered that influenza viruses mutated leading to antigenic changes. Since 1973, the WHO has issued annual recommendations for the composition of the influenza vaccine based on results from surveillance systems that identify currently circulating strains. In 1978, the first trivalent vaccine included two influenza A strains and one influenza B strain. Currently, there are two influenza B strains circulating and there is a quadrivalent influenza vaccination available.

The influenza viruses in the seasonal flu vaccine are selected each year based on surveillance data indicating which viruses are circulating and forecasts about which viruses are the most likely to circulate during the coming season. The degree of similarity between available vaccine viruses and circulating viruses also is important. Vaccine viruses must be similar to the influenza viruses predicted to circulate most commonly during the upcoming season. Influenza A viruses are in a perpetual state of change. Spontaneous changes called mutations occur frequently in the genes of the Influenza A virus. From one flu season to the next, genetic changes in the circulating influenza A viruses are extensive enough to cause the virus to go unrecognized by the immune system — even if you had the flu shot or the flu the previous year. This is why you need a flu shot every year; the shot from the previous year cannot protect you against the newly mutated influenza A virus.

What Influenza strains make up the 2016-2017 vaccination?
The 2016-2017 Influenza Vaccine:

On March 4, 2016, the Food and Drug Administration’s Vaccines and Related Biologics Advisory Committee (VRBPAC) endorsed the WHO-recommended vaccine viruses for use in all U.S. seasonal flu vaccines for the 2016-2017 flu season. It was recommended that trivalent vaccines for use in the 2016-2017 influenza season (Northern Hemisphere winter) contain the following:

an A/California/7/2009 (H1N1)pdm09-like virus;
an A/Hong Kong/4801/2014 (H3N2)-like virus;
a B/Brisbane/60/2008-like virus (B/Victoria lineage).

It was recommended that quadrivalent vaccines containing two influenza B viruses contain the above three viruses and a B/Phuket/3073/2013-like virus (B/Yamagata lineage).
Vaccination Coverage during 2015-2016 Season:
Influenza Activity — United States, 2015–16 Season and Composition of the 2016–17 Influenza Vaccine. Davlin SL, Blanton L, Kniss K, et al. Influenza Activity — United States, 2015–16 Season and Composition of the 2016–17 Influenza Vaccine. MMWR Morb Mortal Wkly Rep 2016;65:567–575. DOI:

Do discuss the influenza vaccination with your healthcare team.  Each of us has the opportunity to decrease the risk of having the flu and of transmitting these highly contagious influenza viruses  to dozens of others who can then pass the virus on to more people. It is not just how virulent the Influenza A virus strain is each year that matters, it is what we choose to do as ethical and moral members of our community.

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  • Dr. Pat October 31, 2016 at 2:59 pm

    Dear Holly,
    How kind of you to read and comment. I hope this information helps the readers to understand more about the reasons for influenza vaccination and encourage them to have their annual vaccination.
    Dr. Pat

  • Holly Day October 31, 2016 at 10:10 am

    Thank you, once again, Dr. Allen for this interesting history and good advice.