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Influenza (Flu)

What is it?

Influenza (flu) is a contagious disease caused by influenza viruses. Although flu can be mild, it can also cause severe illness and even death.
You may have heard people describe an illness by saying "flu-like symptoms," but what does that mean?

The most common flu symptoms are fever, chills, muscle aches, cough, sore throat, headaches, and fatigue (being tired).
The efficacy of the vaccine depends on how well the vaccine matches the circulating strains. In the 2019-2020 flu season, vaccination prevented over 100,000 hospitalizations. 
You need a new flu shot every year because the circulating strains change.

For a great video about influenza, click here

Vaccine Options:


Nasal Spray:


What's the difference between them?

All of the flu vaccines are quadrivalent, and none are necessarily better or recommended over others.


Flumist is a nasal spray, not an injection, and it contains live attenuated influenza instead of inactive influenza virus as the active ingredient. This vaccine is approved for people 2-49 years old, but it should not be used in pregnant people or people who are immunocompromised.

Fluad, Flublok, and Fluzone (high-dose) are recommended for people over age 65 because Fluad contains an adjuvant, and the other two contain higher doses of the active ingredients. 


Flucelvax and Flublok are egg-free vaccines. However, people with egg allergies can receive any flu vaccine.


Talk to your doctor about which flu vaccine would be best for you.

To learn more about the types of flu vaccines, click here.

Relevant Terms

  • Adjuvant: a compound added to some vaccines to strengthen the immune response

  • Attenuated: The pathogen is weakened but not completely inactivated. Attenuated pathogens are too weak to cause disease in almost all people.

  • Serotype: a group of strains within a species that share a particular type of surface structure.

  • Quadrivalent: Protects against four different serotypes of the pathogen (in this case, influenza virus)

  • Vaccine Efficacy: how good a vaccine is at preventing infection and severe disease

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