Seasonal Flu Vaccination 101

It’s that time of year again, when everyone starts talking about getting your flu shot. But what’s in a flu shot and does getting a flu shot always work?

Lee Falin, PhD
3-minute read
Episode #24

Seasonal Flu Vaccination 101

by Lee Falin, PhD

Every year, a group of scientists from around the world gather in a secret meeting to decide the fate of the human race. This isn't science fiction and the participants are not actors. They represent mankind's best chance in the fight against seasonal flu.

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The Few, The Proud

As you might have heard, influenza (aka, the flu), is caused by a virus. What you might not know is that every year there are hundreds, if not thousands, of different flu strains that crop up around the world. Each has a slightly different genetic sequence and differs in both its abilities to infect humans and the severity of the symptoms it produces.

Twice a year, scientists from research centers around the world, including the FDA, CDC, WHO, and various other acronyms, combine their flu research in an effort to predict which flu strains are most likely to strike that season. They then share their recommendations with the governments of each country, which in turn authorize the administration of flu vaccines for those strains.

Private manufacturers actually grow the strains and create the vaccines from them, a process that can take several months. This is why when a new strain shows up suddenly and proves to be dangerous or highly infectious, there can be vaccine shortages.

Haven't I Seen Your Face Before?

Just like with the MMR vaccine I discussed last week, the flu vaccine consists of actual flu viruses that are either too weak to cause the flu or completely inactive.

When your immune system sees these particles floating around in your bloodstream, it does two things. First it attacks the particles, wiping them out. At the same time it creates a large-scale group of dormant cells whose job it is to immediately recognize and destroy any similar flu viruses that they come across.

Didn't See That One Coming

Unfortunately, there's no way to be 100% sure that a particular flu strain will infect a large portion of the population, so even if you have these dormant cells floating around, you may be infected with a strain of virus that your body doesn't recognize. This means that you might still get the flu, despite having a flu shot.

Now, you might have heard somebody say something like, "Yeah, but I know this guy, whose cousin's mother had a friend of a neighbor who got the flu from a flu shot." What most likely happened is this person got the flu despite having a flu shot because they were infected with a strain that wasn't part of the vaccine.

Fortunately, even though a particular flu strain might not be part of the vaccination for that season, there's still a chance that your body will be able to fight it off before the infection takes hold. That's because even though the new strain isn't completely identical to the ones in the vaccine, it might be close enough that your immune system will recognize it.

Side Effects Can Include...

Like every other vaccine, the flu vaccine has the potential to cause side effects. The side effect people most worry about is one called Guillain-Barré syndrome. Guillain-Barré syndrome causes temporary muscle weakness and paralysis and most people who develop the syndrome make a full recovery. According to the CDC, between 3,000 and 6,000 people develop this condition in the U.S. each year, whether or not they have the flu vaccine. Studies have shown that there is a slight increased risk (about 1 in 100,000) of developing Guillain-Barré Syndrome from the flu vaccine, but there is also a risk of developing the same condition after getting the flu itself.


So those are the facts surrounding the seasonal flu vaccination. As always, if you have additional questions about the flu virus or how to treat it, you should listen to the podcast What Is the Flu Virus? by my good friend, the House Call Doctor.

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Cartoon Virus and Woman with the Flu images courtesy of Shutterstock

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About the Author

Lee Falin, PhD

Dr. Lee Falin earned a B.S. in Computer Science from the University of Illinois, then went on to obtain a Ph.D. in Genetics, Bioinformatics, and Computational Biology from Virginia Tech.