What is the flu vaccine?

The flu vaccine can help keep you from getting the flu (influenza).

Flu is caused by a virus. When you have the flu, the virus is in your mucus and saliva and can spread to others when you cough or sneeze. People can also get the flu if they touch something with the flu virus on it (like cups, doorknobs, and hands) and then touch their mouth, nose, or eyes.

Outbreaks of flu occur every year, usually in late fall and winter. Flu symptoms tend to start suddenly.

You should get a flu vaccine every year, before the start of flu season. It’s important to try to prevent flu for several reasons:

• Most people with the flu feel sick for a few days and then get better. However, the flu sometimes leads to other infections, such as ear, sinus, and chest infections. Some people get very sick with the flu and may need to be hospitalized.
• You may miss several days of work or school because of the flu.
• Older adults, very young children, people whose immune systems are weak, and people with long-term medical problems, such as heart or lung disease or diabetes, are at risk for more severe symptoms or problems if they get the flu.
• Even if you don’t get very sick with the flu, you could spread it to someone who could have severe symptoms or problems if they get the flu.

Flu season usually starts in October and may last through May. It takes about 2 weeks before the flu vaccine can fully protect you against the flu. The vaccine is changed each year to protect against the kinds of flu virus that are expected to be most common during the next flu season. You can still get the vaccine after the flu season starts to help protect you against the flu.

How is the flu vaccine given?

The flu vaccine can be given as a nasal spray or as a shot in the arm.

The nasal spray can be given to healthy people age 2 to 49 who are not pregnant. The nasal spray prevents 4 strains of flu. If you get the nasal spray form of the vaccine, you may be able to spread the virus to other people for up to 1 week. Stay away from people at risk of getting very sick from the flu, such as babies, pregnant women, and people with weakened immune systems or a long-term disease, such as diabetes, during this time.

There are several types of flu shots:

• A shot that protects against either 3 or 4 strains of flu is available for people ages 6 months and older.
• A shot that protects against 3 strains of flu, using a very small needle, is available for people ages 18 to 64.
• A high-dose shot that protects against 3 strains of flu is available for people over age 65.
• A shot that protects against 3 strains of flu is available for people with a severe egg allergy that are age 18 to 49.

Ask your healthcare provider which form of the flu vaccine is right for you.

How does it work?

The vaccine exposes your immune system to the flu virus. The immune system is your body’s defense against infection. Your body reacts to the vaccine by making special cells (antibodies) that can fight it.

The vaccine itself will not give you the flu. However, if you were exposed to the flu just before getting the vaccine, you may still get sick. If you do get the flu after getting the vaccine, you will not get as sick as you would have without the vaccine.

Who should get the flu vaccine?

Adults and children 6 months or older should get the flu vaccine. This is especially important for people at high risk of serious flu complications, such as:

• Young children
• Pregnant women
• People with long-term health problems, like asthma, diabetes, heart or lung disease, or a weakened immune system
• People with certain muscle or nerve disorders, such as seizure disorders or cerebral palsy, who are at higher risk for breathing or swallowing problems
• People 65 years old and older

The flu vaccine is also especially important for healthcare workers and others who live with or care for those who are at high risk of complications. The vaccine will help keep them from spreading the flu to the people they are caring for.

Talk with your healthcare provider before getting the vaccine if you:

• Are sick with a fever
• Had Guillain-Barré syndrome (GBS) within 6 weeks after getting the flu vaccine
• Have ever had a severe allergic reaction to eggs or to a previous flu shot. Eggs are used to make some kinds of flu vaccine. Ask about the egg-free vaccine called Flublok that is available for people ages 18 to 49.

It’s OK to get the vaccine if you have a cold.

Thimerosal is a preservative used in some flu shots. Thimerosal-free vaccine is available if you are allergic to thimerosal or are concerned about its safety. The nasal flu vaccine does not contain thimerosal.

What are the side effects of the vaccine?

You cannot get the flu from the flu vaccine. The flu vaccine can sometimes cause minor side effects, such as:

• Soreness, redness, or swelling where the shot was given
• Mild fever
• Body aches

These symptoms may start a few hours after the vaccination and last a day or two.

Serious problems from the flu vaccine, such as severe allergic reactions, are very rare.