The flu vaccine changes from year to year and its efficacy varies. Here’s why.
Does the Flu Shot Work?
Published January 17, 2018
Onscreen : This season’s flu strain has already killed hundreds of Americans. Even some people who get a flu shot still get sick. Why? Let’s start with the influenza virus.
Sarah Cobey : The flu is very serious. It can kill you.
Onscreen : The flu is so dangerous because it mutates (changes) frequently.
Cobey : This is partly what allows influenza to escape immunity.
Onscreen : And why we make a new vaccine each year.
Cobey : The point is to give us the best protection possible to what’s circulating.
Onscreen : The vaccine contains parts of the virus, so they can teach your immune system to target the real virus with antibodies.
Cobey : The W.H.O. [World Health Org.] meets twice a year to decide on which strains will be included in the influenza vaccine. Once these strains are chosen, they’re then grown in chicken eggs. The virus grows well in eggs, and so this allows us to harvest a lot of virus.
Onscreen : It takes a long time (~9 months) to choose the strains, grow the virus, and produce the vaccine. Eventually it becomes part of the flu shot. But viruses and antibodies evolve to outsmart each other.
In 2014-15, one flu strain mutated, adding a sugar to its surface. Old antibodies (from old vaccines) no longer recognized it. In 2016-17, vaccine makers started growing the new virus in chicken eggs, as usual. But something about the eggs made the vaccine virus mutate again and lose the sugar.
Cobey : So that meant that the vaccine had less protection than it could have. Egg adaptations have been a problem for a long, long time.
Onscreen : The W.H.O. must decide far ahead which strains to include in the vaccine. For both these reasons, people may catch the flu even with a flu shot. The vaccine can still help, possibly making symptoms less severe. But can we make a more reliable vaccine?
Cobey : The good news is now, for the first time we have a lot of vaccines available that are grown using an entirely different process.
Onscreen : Alternatives to eggs, like dog kidney cells and larval moth cells, can shorten the production timeline and reduce mutations.
Some argue we remain at high risk for a devastating flu pandemic. And that perhaps the answer lies in developing a universal flu vaccine.
For more information about the flu, visit: cdc.gov/flu
- Writing & Research
- Theresa Machemer
- Digital Producer
- Ari Daniel
- Editorial Review
- Julia Cort
- Special Thanks
- Centers for Disease Control and Prevention
- © WGBH Educational Foundation 2018
- Visuals & Videography
David W. Held
Centers for Disease Control and Prevention
Flickr/ CC BY-NC 2.0 | Carlos Villarreal
wikipedia | Thorkild Tylleskar, Timisstuck, WHO
- Sound Effects
- (main image: flu virus and antibodies)