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).
Flu viruses are always present somewhere in the world. In the United States flu outbreaks most
often 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 36,000 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 given as a shot has been inactivated, or "killed." This means you
cannot catch the flu from getting a shot. Getting the shot introduces part of the inactive 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.
Who should get the flu vaccine?
In general, anyone who wants to reduce their chances of getting the flu can get the flu shot. Some
people need to be sure to get the shot every year. They are either people who are at high risk of
having serious flu complications or people who live with or care for people at high risk for
serious complications. Groups of people who should get the flu vaccine every year are:
children aged 6 to 59 months (just under 5 years old)
people 50 years old or older
people with chronic medical problems, such as asthma, heart disease, chronic obstructive
pulmonary disease (COPD), and diabetes
people who live in nursing homes and other long-term care facilities
people whose immune systems may be impaired, such as by HIV, cancer, or an organ
people working in healthcare
people who live with or care for others at high risk for complications from flu
household contacts and other caregivers of children less than 6 months of age (these
children are too young to be vaccinated).
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.
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.
Who should not get the flu vaccine?
Talk with your healthcare provider before getting a flu shot if you:
have ever had a severe allergic reaction to eggs or to a previous flu shot (eggs are used to
help make flu vaccine)
have a history of Guillain-Barré syndrome (GBS)
are sick with a fever.
It is OK to get the vaccine if you just have an upper respiratory infection--that is, a cold--without
Some vaccine 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.
What is FluMist?
A nasal spray called FluMist is another way to get the flu vaccine. Adults can use this nasal
spray if they are healthy, not pregnant, and under age 50. 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
some other medical conditions cannot take the nasal spray.
When should I get the flu vaccine?
The flu vaccine becomes effective 1 to 2 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,
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?
For people who do not have egg or thimerosal allergies, the flu vaccine has infrequent, minor
side effects, such as:
soreness, redness, or swelling where the shot was given
If these problems occur, they start soon after the shot. They may last 1 to 2 days.
Signs of a serious allergic reaction can include breathing problems, hoarseness or wheezing,
hives, paleness, weakness, a fast heartbeat, or dizziness. An allergic reaction may occur within a
few minutes to a few hours after the shot.
If you think you are having a serious reaction to the flu vaccine, call your healthcare provider
right away. Tell them when you received the vaccine and what your symptoms are. Ask if your
provider needs to see you.