Questions & Answers: Seasonal Flu Shot

 

What is the flu shot?

The flu shot is an inactivated vaccine (containing killed virus) that is given with a needle, usually in the arm. It contains three influenza viruses. The three vaccine strains – one A (H3N2) virus, one A (H1N1) virus, and one B virus – are representative of the influenza vaccine strains recommended for that year. Viruses for the flu shot are grown in eggs.

Who should get a flu shot?

In general, anyone who wants to reduce their chances of getting the flu can get vaccinated. However, certain people should get vaccinated each year. They are either people who are at high risk of having serious flu complications or people who live with or care for those at high risk for serious complications. During flu seasons when vaccine supplies are limited or delayed, the ACIP makes recommendations regarding priority groups for vaccination.

People who should get vaccinated each year are:

1. People at high risk for complications from the flu, including:
   • Children aged 6 months until their 5th birthday,
   • Pregnant women,
   • People 50 years of age and older, and
   • People of any age with certain chronic medical conditions;
   • People who live in nursing homes and other long term care facilities.
     
     
2. People who live with or care for those at high risk for complications from flu, including:
   • Household contacts of persons at high risk for complications from the flu (see above)
   • Household contacts and out of home caregivers of children less than 6 months of age (these children are too young to be vaccinated)
   • Healthcare workers.

Use of the Nasal Spray Flu Vaccine?

It should be noted that vaccination with the nasal-spray flu vaccine is always an option for healthy persons aged 5-49 years who are not pregnant.

Who should not get a flu shot?

Talk with a doctor before getting a flu shot if you:
1) Have ever had a severe allergic reaction to eggs or to a previous flu shot
or
2) Have a history of Guillain-Barré syndrome (GBS).

If you are sick with a fever when you go to get your flu shot, you should talk to your doctor or nurse about getting your shot at a later date. However, you can get a flu shot at the same time you have a respiratory illness without fever or if you have another mild illness.

How effective is the flu shot?

With the flu shot, when the "match" between vaccine and circulating strains is close, the vaccine prevents influenza in about 70%-90% of healthy persons younger than age 65 years. Among elderly persons living outside chronic-care facilities (such as nursing homes) and those persons with long-term (chronic) medical conditions, the flu shot is 30%-70% effective in preventing hospitalization for pneumonia and influenza. Among elderly nursing home residents, the flu shot is most effective in preventing severe illness, secondary complications, and deaths related to the flu. In this population, the shot can be 50%-60% effective in preventing hospitalization or pneumonia and 80% effective in preventing death from the flu.

What are the risks from getting a flu shot?

The viruses in the flu shot are killed (inactivated), so 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

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 the influenza vaccine are grown in hens' eggs. People who have had a severe reaction to eggs or to a flu shot in the past should not get a flu shot before seeing a physician.
  
  
• Guillain-Barré syndrome: Normally, about one person per 100,000 people per year will develop Guillain-Barré syndrome (GBS), an illness characterized by fever, nerve damage, and muscle weakness. In 1976, vaccination with the swine flu vaccine was associated with getting GBS. Several studies have been done to evaluate if other flu vaccines since 1976 were associated with GBS. Only one of the studies showed an association. That study suggested that one person out of 1 million vaccinated persons may be at risk of GBS associated with the vaccine.

More facts about potential side effects of the influenza vaccine can be found in Prevention & Control of Influenza - Recommendations of the Advisory Committee on Immunization Practices (ACIP). MMWR 2007 Jul 13;56(RR06):1-54. Also available as PDF (720K).

What should I do if I have had a serious reaction to 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.

Content Source: Coordinating Center for Infectious Diseases (CCID)