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VERIFY: How effective is the flu vaccine?

After a viewer's relative got the flu shot but wound up with the flu 2 years in a row, she asked VERIFY if the government tracks how many people that happens to.

Every year we’re asked if the flu shot is really effective and one of you wanted to know how we answer that question.  

Viewer Rita W. asked VERIFY, “How many of the people that get sick with the flu have had flu shots?” She added her son-in-law got the flu two years in a row after receiving the flu shot and asked us if there are actual surveys for this.

Credit: VERIFY


Are there surveys that study flu vaccine efficiency? How many people that get sick with the flu have had flu shots?


we can VERIFY that the government does keep track of how effective the flu vaccine is, but there isn’t a specific nationwide total of how many people get the flu vaccine and still get sick. 

Instead, the CDC focuses on research studies in target cities to determine an estimated average rate for the nation as a whole. 

Using that data, the CDC says the flu vaccine can reduce the risk of a person getting the flu between 40% and 60%.


Each year, studies are conducted to determine the efficacy of that season’s flu vaccine. In the past 10 years, the most effective vaccine was in 2010-11 when it was 60% effective. The least effective was the vaccine from 2014-15 when it was estimated to be only 19% effective.

The CDC uses three different networks to study effectiveness. One focuses on the general adult population, one focuses on older adults and one network focuses on children. These studies target individual states and cities rather than surveying people nationwide.

These studies compare the frequency of influenza vaccinations among patients who have the flu, to vaccinations in a comparable group that does not have the flu.

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Despite these studies, the CDC does not have data on the total number of people nationwide who get the flu after receiving a flu vaccine. The closest we get to that are these effectiveness studies.

According to the CDC, the vaccine’s effectiveness can vary from year to year depending on the virus. Flu vaccines are designed to protect against certain strains that researchers predict will spread that season. Since there are multiple strains of flu viruses that are constantly evolving, it’s possible a different flu virus begins spreading than the one the vaccine protects against. The vaccine’s effectiveness can also vary from person to person depending on their age and health.

There are benefits to the flu vaccine other than preventing you from getting sick. The CDC says the vaccine can help reduce the severity of the flu once you get it. They cite a study from 2017 and another one from 2018 that looked at things like intensive care unit visits and length of stay at hospitals.

So yes, it’s still possible to get the flu after receiving a flu shot, like what happened in Rita’s situation. However, by getting the flu vaccine the likelihood you will get the flu is reduced and the severity of your sickness is typically reduced, if you happen to still get sick. 

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