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Flu (Influenza)

What is it?

Flu (influenza) is a contagious respiratory illness caused by influenza viruses that infect the nose, throat, and lungs. It can cause mild to severe illness and can lead to hospitalization and death. Every year in the United States, millions of people are sickened, hundreds of thousands are hospitalized, and thousands or tens of thousands die from the flu.

Anyone can get the flu (even healthy people), and serious problems related to the flu can happen at any age — but some people are a higher risk of developing serious flu-related complications if they get sick. This includes people 65 years and older, people of any age with certain chronic medical conditions (such as diabetes, asthma, or heart disease), pregnant women, certain racial and ethnic minority groups, and young children.


  • Fever (not everyone with flu will have a fever) or feeling feverish
  • Chills
  • Cough
  • Sore throat
  • Runny or stuffy nose
  • Headache
  • Muscle or body aches
  • Tiredness
  • Vomiting and/or diarrhea (this is more common in children than adults)

How does it spread?

Through the sneezing or coughing of an infected person; experts also think you can get the flu by touching a surface that has flu germs on it and then touching your mouth or nose.

Your best protection is vaccination

The best and most important step to prevent the flu is by getting a flu vaccine each year. The CDC recommends that everyone 6 months of age and older get a flu vaccine each year. Flu vaccination can reduce flu illnesses, doctors’ visits, and missed work and school due to flu, as well as prevent flu-related hospitalizations. You should get a flu vaccine by the end of October each year. However, as long as flu viruses are circulating, vaccination should continue throughout flu season, even in January or later. Flu vaccines are offered in many locations. Even if you don’t have a regular doctor or nurse, you can get a flu vaccine somewhere else, including doctor’s offices, community clinics, health departments, retail stores, pharmacies, and student health centers, as well as by many employers and schools.


Recommended for everyone over 6 months of age, every year; there are various types of flu vaccine. Seasonal influenza shots protect against the three or four influenza viruses that research indicates will be most common during the season.

Quadrivalent Standard Dose Vaccine
Designed to protect against four different flu viruses

High-Dose Flu Vaccine
Contains 4 times the amount of antigen as a regular flu shot and is licensed specifically for people 65 years and older

Adjuvanted Vaccine
Made with an additive that creates a stronger immune response and is licensed specifically for people 65 years and older

Cell-Based Flu Vaccines
Grown in cultured cells of mammalian origin instead of in hens' eggs

Recombinant Flu Vaccines
Produced using a method that does not require an egg-grown vaccine virus

Intradermal Influenza (Flu) Vaccine
Injected into the skin instead of the muscle

Nasal Spray Flu Vaccine
Live Attenuated Influenza Vaccine [LAIV] is given as a nasal spray

Flu Vaccination by Jet Injector
Approved for use in people 18 through 64 years of age