Flu (influenza) is caused by viruses that attack the lungs, nose, and throat. This group of viruses is very different from those that cause stomach upset and diarrhea–or what some call the “stomach flu.”

Flu symptoms can be mild or severe, but typically cause a cough, sore throat, body aches, and fever.

Usually flu is more severe than a cold, and symptoms start very suddenly

Most healthy people will recover from flu without complication; however, many people are in an age group or have a condition that places them at high risk for complications from flu.

These groups include:
• Children under age 5 years, but especially those under 2 years
• Adults over age 65 years
• Pregnant people
• People with a chronic medical condition, such as asthma, neurological and neurodevelopmental conditions, lung and heart disease, chronic kidney disease and diabetes, weakened immune system, and obesity (especially those with BMI ≥40).

Flu vaccines cause antibodies to develop in the body about two weeks after vaccination. These antibodies provide protection against infection with circulating influenza viruses.

Seasonal flu vaccines are designed to protect against the influenza viruses that research indicates will be most common during the upcoming season.

Efficacy can vary based on things like how healthy you are, how old you are, and whether you've been vaccinated before.

While the vaccine won't prevent every case of flu, it is the most specific tool we have against the flu. Even in years when efficacy is low, influenza vaccination prevents severe disease and death.

Year after year, flu vaccine is shown to be safe. They have been extensively studied for safety and are continuously monitored for safety.

Current guidance for the use of COVID-19 vaccines indicates that these COVID-19 vaccines can be co-administered with other vaccines, including influenza vaccines.

September and October are generally good times to be vaccinated against flu. Ideally, everyone should be vaccinated by the end of October.

Additional considerations concerning the timing of vaccination for certain groups include:

• Adults, especially those 65 years and older, should generally not get vaccinated early (in July or August) because protection may decrease over time, but early vaccination can be considered for any person who is unable to return at a later time to be vaccinated.
• Children can get vaccinated as soon as vaccine becomes available, even if this is in July or August. Some children need two doses of flu vaccine. For those children it is recommended to get the first dose as soon as vaccine is available, because the second dose needs to given at least 4 weeks after the first.
• Early vaccination can also be considered for people who are in the third trimester of pregnancy, because this can help protect their infants during the first months of life (when they are too young to be vaccinated).

While a flu vaccine cannot give you flu illness, there are different side effects that may be associated with getting a flu shot or a nasal spray flu vaccine. These side effects are usually mild and short-lasting, especially when compared to symptoms of flu.

A flu shot: The viruses in a flu shot are killed (inactivated), so you cannot get flu from a flu shot.

Some common but minor side effects include:

• Pain or redness at the injection site
• Muscle aches
• Headache
• Mild fever

*These symptoms usually resolve in a day or two and should not be mistaken for flu disease.

Everyone 6 months and older should get a flu vaccine every season with rare exceptions. If you have concerns or questions, please speak with your provider.

*Information about who cannot get a flu vaccine and who should talk to their doctor before getting a flu vaccine is available at Who Should & Who Should NOT Get Vaccinated.