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FAQs: Is There More Than One Flu Virus?

Posted on February 18, 2021
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While the flu vaccine has been safely used for more than 50 years, there are still a lot of questions around the flu virus and the vaccines. In this post, we’ll answer common questions about the flu and flu shot from our Facebook and Twitter communities.

Is there more than one flu virus?

There are four types of influenza viruses – A, B, C and D – but only three are known to infect people. Influenza D primarily affects cattle. Seasonal flu is caused by influenza A and influenza B viruses. Influenza A can also cause global flu pandemics, such as H1N1. Influenza C only causes mild illness. Because flu strains can change slightly from year to year (known as “antigenic drift”), flu vaccines are updated annually to provide the best protection against circulating strains.

How does the flu vaccine protect against different types of flu?

Circulating flu viruses can change every year. Global, year-round surveillance to identify circulating flu strains is conducted by the World Health Organization, CDC, and other organizations. Every year this information is used to select the flu viruses that are included in the manufacturing of annual flu vaccines. Because viruses can change and an individual’s immunity from flu vaccination declines over time, it’s important to get a flu vaccine each and every year.

How does the flu vaccine prevent the flu?

Flu vaccines protect against seasonal flu by creating antibodies that teach your body how to fight off the flu. Each seasonal vaccination includes inactive strains of influenza A and B to help protect you against circulating flu strains. Everyone 6 months and older should get an annual flu vaccination.


Check out our Flu Facts to learn more.

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