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Seasonal Flu Shot

Questions & Answers

Visit What You Should Know for the 2014-2015 Influenza Season for flu and flu vaccine information specific to the 2014-15 flu season.

What is the flu shot?

The flu shot is a vaccine given with a needle, usually in the arm. The seasonal flu shot protects against the three or four influenza viruses that research indicates will be most common during the upcoming season.

Is there more than one type of flu shot available?

There are several flu vaccine options for the 2014-2015 flu season.

Traditional flu vaccines made to protect against three different flu viruses (called “trivalent” vaccines) are available. In addition, flu vaccines made to protect against four different flu viruses (called “quadrivalent” vaccines) also are available.

Trivalent flu vaccine protects against two influenza A viruses (an H1N1 and an H3N2) and an influenza B virus. The following trivalent flu vaccines are available:

The quadrivalent flu vaccine protects against two influenza A viruses and two influenza B viruses. The following quadrivalent flu vaccines are available:

(*”Healthy” indicates persons who do not have an underlying medical condition that predisposes them to influenza complications.)

Who should get vaccinated this season?

Everyone who is at least 6 months of age should get a flu vaccine this season. This recommendation has been in place since February 24, 2010 when CDC’s Advisory Committee on Immunization Practices (ACIP) voted for “universal” flu vaccination in the United States to expand protection against the flu to more people.

While everyone should get a flu vaccine this season, it’s especially important for some people to get vaccinated.

Those people include the following:

  • People who are at high risk of developing serious complications (like pneumonia) if they get sick with the flu.
  • People who live with or care for others who are at high risk of developing serious complications (see list above).
    • Household contacts and caregivers of people with certain medical conditions including asthma, diabetes, and chronic lung disease.
    • Household contacts and caregivers of infants younger than 6 months old.
    • Health care personnel.

More information is available at Who Should Get Vaccinated Against Influenza.

Special Consideration Regarding Egg Allergy:

People who have ever had a severe allergic reaction to eggs may be advised not to get vaccinated. People who have had a mild reaction to egg—that is, one which only involved hives—may receive a flu shot with additional precautions. Make sure your health care provider knows about any allergic reactions. Most, but not all, types of flu vaccine contain small amount of egg.

Who should not get a flu shot?

Influenza vaccine is not approved for children younger than 6 months of age.

People who have had a severe allergic reaction to influenza vaccine should generally not be vaccinated.

There are some people who should not get a flu vaccine without first consulting a physician.

These include:

  • People who have a moderate-to-severe illness with or without a fever (they should wait until they recover to get vaccinated), and
  • People with a history of Guillain–Barré Syndrome (a severe paralytic illness, also called GBS) that occurred after receiving influenza vaccine and who are not at risk for severe illness from influenza should generally not receive vaccine. Tell your doctor if you ever had Guillain-Barré Syndrome. Your doctor will help you decide whether the vaccine is recommended for you.

How effective is the flu shot?

The ability of a flu vaccine to protect a person depends on the age and health status of the person getting the vaccine, and the similarity or “match” between the viruses or virus in the vaccine and those in circulation. For more information, see Vaccine Effectiveness – How well does the Flu Vaccine Work.

What are the risks from getting a flu shot?

You cannot get the flu from a flu shot. The risk of a flu shot causing serious harm or death is extremely small. However, a vaccine, like any medicine, may rarely cause serious problems, such as severe allergic reactions. Almost all people who get influenza vaccine have no serious problems from it.

What are the side effects that could occur?

  • Soreness, redness, or swelling where the shot was given
  • Fever (low grade)
  • Aches

The intradermal flu shot may cause other additional mild side effects including:

  • Toughness and itching where the shot was given

If these problems occur, they begin soon after the shot and usually last one to two days.

Can severe problems occur?

Life-threatening allergic reactions are very rare. Signs of serious allergic reaction can include breathing problems, hoarseness or wheezing, hives, paleness, weakness, a fast heartbeat, or dizziness. If they do occur, it is within a few minutes to a few hours after the shot. These reactions are more likely to occur among persons with a severe allergy to eggs, because the viruses used in most influenza vaccines are grown in hens’ eggs. While severe reactions are uncommon, you should let your doctor, nurse, clinic, or pharmacist know if you have a history of allergy or severe reaction to flu vaccine or any part of flu vaccine, including eggs.

There is a small possibility that influenza vaccine could be associated with Guillain-Barré syndrome, no more than 1 or 2 cases per million people vaccinated. This is much lower than the risk of severe complications from flu, which can be prevented by flu vaccine.

What should I do if I have had a serious reaction to seasonal influenza vaccine?

Call a doctor, or get to a doctor right away.

Tell your doctor what happened, the date and time it happened, and when you got the flu shot.

Ask your doctor, nurse, or health department to file a Vaccine Adverse Event Reporting System (VAERS) form, or call VAERS at 1-800-822-7967.

Can the flu shot give me the flu?

No, a flu shot cannot give you the flu. Flu vaccines that are administered with a needle are currently made in two ways: the vaccine is made either with a) flu vaccine viruses that have been ‘inactivated’ and are therefore not infectious, or b) with no flu vaccine viruses at all (which is the case for recombinant influenza vaccine). In randomized, blinded studies, where some people got flu shots and others got saltwater shots, the only differences in symptoms was increased soreness in the arm and redness at the injection site among people who got the flu shot. There were no differences in terms of body aches, fever, cough, runny nose or sore throat.

More information about these studies is available at:

Why do some people not feel well after getting the flu shot?

The flu shot can cause mild side effects that are sometimes mistaken for flu. For example, people sometimes experience a sore arm where the shot was given. The soreness is often caused by a person’s immune system making protective antibodies in response to being vaccinated. These antibodies are what allow the body to fight against flu. The needle stick may also cause some soreness at the injection site. Rarely, people who get the flu shot have fever, muscle pain, and feelings of discomfort or weakness. If experienced at all, these effects usually last 1-2 days after vaccination and are much less severe than actual flu illness.

What about people who get a seasonal flu vaccine and still get sick with flu-like symptoms?

There are several reasons why someone might get flu-like symptoms even after they have been vaccinated against the flu.

  1. People may be exposed to an influenza virus shortly before getting vaccinated or during the two-week period that it takes the body to gain protection after getting vaccinated. This exposure may result in a person becoming ill with flu before the vaccine begins to protect them.
  2. People may become ill from other (non-flu) viruses that circulate during the flu season, which can also cause flu-like symptoms (such as rhinovirus).
  3. A person may be exposed to an influenza virus that is not included in the seasonal flu vaccine. There are many different influenza viruses that circulate every year. The flu shot protects against the 3 or 4 viruses (depending on whether the flu shot is a trivalent or quadrivalent vaccine) that research suggests will be most common.
  4. Unfortunately, some people can get infected with an influenza vaccine virus despite getting vaccinated. Protection provided by influenza vaccination can vary widely, based in part on health and age factors of the person getting vaccinated. In general, the flu vaccine works best among young healthy adults and older children. Some older people and people with certain chronic illnesses may develop less immunity after vaccination. However, even among people who tend to respond less well to vaccination, the flu vaccine can still help prevent influenza. Vaccination is particularly important for people at high risk of serious flu-related complications and for close contacts of high-risk people. For more information about the effectiveness of the flu vaccine, see How Well Does the Seasonal Flu Vaccine Work?

Lastly, the flu shot can cause mild side effects that are sometimes mistaken for flu. See ‘Why do some people not feel well after getting the flu shot?’ for more information.

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