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Mount Minutes – Why Does the Flu Vaccine Change Every Year?

November 30, 2019

I’m Katie Dye, biology professor here at
the Mount. Healthcare providers recommend that you get an influenza
vaccine every year. Many people question this, thinking I got a flu shot last year
isn’t that good enough? Today we’ll consider why the flu vaccine changes
yearly. Now, you’ve probably heard the influenza vaccine is based on a guess,
but that term vastly underestimates the efforts of the global healthcare
community. Over 100 countries participate in year-round surveillance, tracking which
strains of the virus are most prevalent in order to predict which strains will
be circulating during the upcoming flu season. Each February, a WHO committee
meets to compile the global data. They make recommendations to the US FDA, who
tells vaccine producers which strains to include in the vaccine. Sometimes by flu
season the circulating strains have changed and the protection the vaccine
generates no longer matches the flu that we actually run into. Circulating strains
can change through a process called antigenic drift. Now, that’s the
accumulation of mutations in the two proteins that are on the surface of the
virus, hemagglutinin and neuraminidase, abbreviated h and n. These are the
proteins that dictate the subtype name of the flu virus such as h1n1 or h3n2,
which you’ve probably heard of. Now, just FYI, all of those H proteins, regardless
of number, have the same job, just a slightly different shape. One role of the
2013 version of the flu vaccine is to provide your immune system with a
g-rated preview of H1 and H3 so that you can generate antibodies later. If you
catch the flu your antibodies can stick to H1 and H3 and inactivate them and
the virus won’t be able to infect your cells, but as h1 and h3 mutate through
antigenic drift the antibodies that you possess from previous immunizations may
no longer stick to them, so the vaccine has to be altered yearly in order to
keep up with circulating strains and to update your antibody portfolio. So, yes
the flu vaccine is based on a guess, but it’s a very educated guess. Over the last
two years on average it was about fifty five percent effective. Now, while that’s
a failing grade in my classes, I’ll gladly take those odds to avoid getting
the flu.

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