Flu shots

What is the flu?

The flu (influenza) is a contagious respiratory illness caused by flu viruses. It is not the same thing as “stomach flu,” which is an intestinal infection that can cause diarrhea, cramps, nausea, and vomiting. Flu symptoms include:

  • Fever or chills
  • Cough
  • Sore throat
  • Runny or stuffy nose
  • Muscle or body aches
  • Headache
  • Fatigue

The flu is a serious illness. Millions of people get the flu every year, and hundreds of thousands of people are hospitalized with flu symptoms. In fact, tens of thousands of people die from flu-related causes each year. 

Even very healthy people can get very sick from the flu and spread it to others.

Why get a flu shot every year?

A seasonal flu shot is the most important step you can take to protect against flu viruses. Flu season can begin as early as October and can continue through May.

Benefits of a flu shot:

  • Eliminate or reduce flu illnesses and symptoms
  • No missed work or school
  • Reduce the risk of flu-related hospitalizations
  • Prevent the spread of flu in the community

Each year, new flu vaccine is developed—based on research that shows which types of flu viruses will be most common during the upcoming flu season.

That’s why getting a flu shot each year is so important—it protects you against the strains of flu that are most likely to infect you during flu season.

How does a flu shot work?

Flu vaccine causes antibodies to develop in the body about two to three weeks after getting a flu shot. These antibodies protect you against infection from the most likely types of flu viruses in the upcoming flu season.

Who should get a flu shot?

  • Everyone who is six months of age and older should get flu vaccine every year.
  • People who are at high risk for serious flu complications include:
    • Pregnant women
    • People age 65 and older
    • People with chronic health conditions such as asthma, diabetes, or heart and lung disease
  • Infants younger than six months old are at risk for serious flu illness, but they are too young to be vaccinated. People who care for young infants should get a flu shot.
  • A flu shot also is important for health-care workers and others who live with or care for people who are at high risk for flu complications.

Will a flu shot give me the flu?

No—a flu shot cannot cause influenza. Flu vaccines given by a shot are made in two ways:

  • Produced from an “inactivated” virus, meaning it’s not infectious
  • Produced with no flu vaccine viruses at all

Some people may have a low-grade fever, headache, or muscle aches after a flu shot, but these symptoms usually go away after one or two days. The most common side effects from a flu shot are soreness, redness, or swelling at the spot where the shot was given.

Can the flu shot make me sick?

Will the flu vaccine make you sick? Find out in under a minute from family medicine specialist Jason Powers, MD, in the newest Influenza in a Minute.

When should you get your flu vaccination?

Timing is everything, at least it is when it comes to receiving your annual flu vaccination. The Centers for Disease Control and Protection (CDC) recommends getting vaccinated before the end of October; however, getting vaccinated too early in the season (for example, July or August) may mean reduced protection against the flu later in the season. Children who need two doses of vaccine to be protected should start the vaccination process sooner, because these doses must be given at least four weeks apart.

The vaccine takes about two weeks to develop antibodies in your system to provide protection against the flu, so receiving yours before the end of October, gives your body time to build up its defenses before peak flu season hits.

Last reviewed: 
November 2021

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