Flu Shots (Influenza Vaccine)

What are flu shots?

When you get a flu shot you are injected in the arm with the influenza vaccine. The vaccine helps protect adults and children from getting influenza (flu).

The influenza virus is always present somewhere in the world. In the United States flu outbreaks tend to occur each year between October and March.

Influenza causes a coldlike upper respiratory infection. Unlike most colds, however, the flu often causes fever, muscle aches, and dizziness. It can also lead to more serious infections, such as pneumonia. Complications from flu cause up to 40,000 deaths per year in the US. These deaths usually occur among older adults and people who have chronic health problems, such as heart disease and severe asthma.

How do they work?

The formula for the flu vaccine is changed every year according to the recommendations of scientists from the Centers for Disease Control (CDC). They predict which strains of flu virus are most likely to appear the next winter.

The virus in the flu vaccine has been inactivated, or "killed." This means you cannot catch the flu from getting a shot. Getting the shot introduces part of the flu virus to your immune system. Your body then reacts by making protective antibodies against the virus.

How effective are they?

Flu shots are usually about 70% effective in preventing flu. Even if you do get the flu, the vaccine helps protect against severe and possibly life-threatening infection. For this reason it is said that the flu shot protects against death from the flu more than from flu itself.

Are there other ways to get the vaccine?

A new alternative to flu shots is FluMist. It is a nasal spray form of the vaccine for healthy adults under 50 years of age. It costs more than the shot. As with flu shots, you will need a new dose of FluMist every year. Unlike the shot, FluMist is a live virus vaccine. For this reason pregnant women and people with weakened immune systems, asthma, or certain other medical conditions cannot take the nasal spray.

When should I get the flu vaccine?

The flu vaccine becomes effective 2 to 4 weeks after you get the shot. It is best to get the flu shot in October of each year, before the flu season begins. Try to get the shot no later than November, if possible.

Flu seasons can vary from region to region. If you are at high risk from infection and plan to travel to an area where you might be exposed to the flu, make sure you have an up-to-date flu shot before you go on your trip.

What are the side effects?

Eggs are used in the production of flu vaccine. If you are allergic to eggs, you may have a severe allergic reaction to the flu shot. The flu vaccine should not be taken by anyone who has a history of severe egg allergy or a previous serious allergic reaction to the flu shot. Also, the flu vaccine is not recommended for people who have had Guillain Barré syndrome (GBS). You should not get a flu shot if you are ill with high fever, but it is okay to get it if you just have an upper respiratory infection, that is, a cold.

Some manufacturers also recommend not getting a flu shot if you have an allergy to thimerosal. Thimerosal is a preservative used in contact lens solutions and the flu vaccine. It is in other vaccines as well.

For people who do not have egg or thimerosal allergies, the flu vaccine has infrequent, minor side effects. The most common reaction is some soreness at the site of the shot. A few people develop fever or muscle aches within a few hours of the injection. These symptoms may last 1 to 2 days.

There have been no reports of flu shot complications affecting the nervous system since the 1976-1977 swine flu epidemic.

Who should get the flu vaccine?

Several groups of people should receive the flu vaccine every year:

people over the age of 50
people whose immune systems may be impaired, such as by HIV, cancer, or an organ transplant
people with chronic medical problems, such as asthma, heart disease, emphysema, and diabetes
people working in health care
school teachers and other community workers with close, daily contact with the public.

Normally, women who are pregnant should get the shot after 13 weeks of pregnancy. However, if they have other chronic medical problems, it is OK to get the shot earlier in the pregnancy.

Flu shots can be helpful for anyone who is not severely allergic to eggs. However, when there is a shortage of flu vaccine, the recommendations for who should get a shot may change, based on the severity of the shortage.

Disclaimer: This content is reviewed periodically and is subject to change as new health information becomes available. The information provided is intended to be informative and educational and is not a replacement for professional medical evaluation, advice, diagnosis or treatment by a healthcare professional.

HIA File GEN4441F.HTM Release 9.0/2006