Flu shot: Your best bet for avoiding influenza

Getting a flu shot often protects you from coming down with the flu. And although the flu shot doesn't always provide total protection, it's worth getting.

By Mayo Clinic Staff

This year's annual flu shot will offer protection against three or four of the influenza viruses expected to be in circulation this flu season. A high-dose flu vaccine also will be available for adults age 65 and older.

Influenza is a respiratory infection that can cause serious complications, particularly to young children, older adults and people with certain medical conditions. Influenza vaccines — though not 100 percent effective — are the best way to prevent the misery of the flu and its complications. The Centers for Disease Control and Prevention (CDC) recommends that everyone 6 months of age or older be vaccinated annually against influenza.

Here are the answers to common questions about flu shots:

When is the flu vaccine available?

The flu vaccine is made by private manufacturers and takes about six months to produce. The availability of the flu vaccine depends on when production is completed, but generally, shipments begin sometime in August. Doctors and nurses are encouraged to begin vaccinating people as soon as the flu vaccine is available in their areas.

It takes up to two weeks to build immunity after a flu shot, but you can benefit from the vaccine even if you don't get it until after the flu season starts. It's usually best for people in the United States to get their flu vaccine by the end of October. However, you can still protect yourself against late flu outbreaks if you get the vaccine in February or later.

Why do I need to get vaccinated every year?

Because flu viruses evolve so quickly, last year's vaccine may not protect you from this year's viruses. New flu vaccines are released every year to keep up with rapidly adapting flu viruses.

When you get vaccinated, your immune system produces antibodies to protect you from the viruses included in the vaccine. But, antibody levels may decline over time — another reason to get a flu shot every year.

Who should get the flu vaccine?

The CDC recommends annual influenza vaccinations for everyone age 6 months or older. Vaccination is especially important for people at high risk of influenza complications, including:

  • Pregnant women
  • Older adults
  • Young children

Children between 6 months and 8 years may need two doses of the flu vaccine, given at least four weeks apart, to be fully protected. A 2017 study showed that the vaccine significantly reduces a child's risk of dying from the flu. Check with your child's health care provider.

Chronic medical conditions also can increase your risk of influenza complications. Examples include:

  • Asthma
  • Cancer or cancer treatment
  • Chronic obstructive pulmonary disease (COPD)
  • Cystic fibrosis
  • Diabetes
  • HIV/AIDS
  • Kidney or liver disease
  • Obesity

Who shouldn't get a flu shot?

Check with your doctor before receiving a flu vaccine if:

  • You're allergic to eggs. Most types of flu vaccines contain a small amount of egg protein. If you have a mild egg allergy — you only get hives from eating eggs, for example — you can receive the flu shot without any additional precautions. If you have a severe egg allergy, you should be vaccinated in a medical setting and be supervised by a doctor who is able to recognize and manage severe allergic conditions.

    There are also flu vaccines that don't contain egg proteins, and are Food and Drug Administration (FDA) approved for use in people age 18 and older. Consult your doctor about your options.

  • You had a severe reaction to a previous flu vaccine. The flu vaccine isn't recommended for anyone who had a severe reaction to a previous flu vaccine. Check with your doctor first, though. Some reactions might not be related to the vaccine.

What are my flu vaccine delivery options?

The flu vaccine will be available as an injection or as a nasal spray. In the past two flu seasons, there was concern that the nasal spray flu vaccine wasn't effective enough against certain types of flu. The nasal spray vaccine is expected to be more effective in the 2018-2019 season.

The nasal spray vaccine is approved for people between 2 and 49 years old.

The nasal flu vaccine isn't recommended for:

  • Children under 2
  • Adults 50 and older
  • Pregnant women
  • Children between 2 and 17 years old who are taking aspirin or a salicylate-containing medication
  • People with weakened immune systems
  • Kids 2 to 4 years old who have had asthma or wheezing in the past 12 months

There are other groups advised to be cautious about the use of a nasal spray flu vaccine. Check with your doctor to see if you fall into one of these groups.

The flu vaccine can also be delivered by an injection that's usually given in a muscle in the arm. If you're an adult under 65, you may also choose an in-the-skin (intradermal) vaccine, or you may prefer to have your vaccine delivered using a jet injector device, which uses a high-pressure, narrow stream of fluid to penetrate the skin instead of a needle.

Can the vaccine give me the flu?

No. The flu vaccine can't give you the flu. But you might develop flu-like symptoms — despite getting a flu vaccine — for a variety of reasons, including:

  • Reaction to the vaccine. Some people experience muscle aches and a fever for a day or two after receiving a flu vaccine. This may be a side effect of your body's production of protective antibodies.
  • The two-week window. It takes about two weeks for the flu shot to take full effect. If you're exposed to the influenza virus shortly before or during that time period, you might catch the flu.
  • Mismatched flu viruses. In some years, the influenza viruses used for the vaccine don't match the viruses circulating during the flu season. If this occurs, your flu shot will be less effective, but may still offer some protection.
  • Other illnesses. Many other illnesses, such as the common cold, also produce flu-like symptoms. So you may think you have the flu when you actually don't.

What kind of protection does the flu vaccine offer?

How well the flu vaccine works can vary. The flu vaccine is generally more effective among people under 65 years old. Some older people and people with certain medical conditions may develop less immunity after receiving a flu shot.

Reviews of past studies have found that, on average, the flu vaccine is about 60 percent effective for adults between 18 and 64 years. The vaccine may sometimes be less effective, but it can also be more effective too. In some years, it can be up to 90 percent effective at preventing the flu.

Even when the vaccine doesn't completely prevent the flu, it may lessen the severity of your illness and the risk of serious complications.

Can I lower my risk of the flu without getting a flu shot?

The flu vaccine is your best defense against the flu, but there are additional steps you can take to help protect yourself from the flu and other viruses. These steps include:

  • Wash your hands often and thoroughly with soap and water.
  • Use an alcohol-based sanitizer on your hands if soap and water aren't available.
  • Avoid touching your eyes, nose or mouth whenever possible.
  • Avoid crowds when the flu is most prevalent in your area.
  • Practice good health habits. Get plenty of sleep, exercise regularly, drink plenty of fluids, eat a nutritious diet and manage your stress.

You can also help prevent the spread of the flu by staying home if you do get sick.

Sept. 11, 2018 See more In-depth