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 as well as an additional vaccine also will be available for adults age 65 and older.

Influenza is a respiratory infection that can cause serious complications, particularly in young children, older adults and people with certain medical conditions. Getting an influenza vaccine — though not 100% effective — is the best way to prevent the misery of the flu and its complications. The Centers for Disease Control and Prevention (CDC) recommends annual flu vaccination for everyone age 6 months or older.

Here are the answers to common questions about flu shots:

When is the flu vaccine available?

Private manufacturers make the flu vaccine and take about six months to produce it. The availability of the flu vaccine depends on when production is completed. But generally, shipments begin sometime in August in the United States. Doctors and nurses may 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 in September and October, and aim to get it 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, the first time they are given a flu vaccine. After that, they can receive single annual doses of the flu vaccine. A 2017 study showed that the vaccine significantly reduces a child's risk of dying of the flu. Check with your child's doctor.

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

Anyone with a chronic medical condition should get the flu vaccine.

Check with your doctor before receiving a flu vaccine if:

  • 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.

If you have an egg allergy, you can still receive the flu vaccine.

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What are my flu vaccine delivery options?

The flu vaccine will be available as an injection or as a nasal spray. In recent years, 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 2020-2021 season.

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

The nasal flu vaccine isn't recommended for some people, including:

  • 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, such as people with certain chronic medical conditions. Check with your doctor to see if you need to be cautious about getting a nasal spray flu vaccine.

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 or other respiratory diseases?

No. The flu vaccine can't give you the flu. It also does not increase your risk of COVID-19. 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 to protect you from the flu 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 the flu vaccine is about 50% to 60% effective for healthy adults who are between 18 and 64 years old. The vaccine may sometimes be less effective.

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

The flu vaccine does not protect you from getting COVID-19. However, it's especially important to get the flu vaccine this season because the flu and coronavirus disease 2019 (COVID-19) cause similar symptoms. Flu vaccination could reduce symptoms that might be confused with those caused by COVID-19. Preventing the flu and reducing the severity of flu illness and hospitalizations could also lessen the number of people needing to stay in the hospital.

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, including COVID-19. These steps include the following:

  • Wash your hands often and thoroughly with soap and water for at least 20 seconds.
  • Use an alcohol-based sanitizer on your hands if soap and water aren't available.
  • Avoid touching your eyes, nose or mouth.
  • Avoid crowds when the flu is spreading in your area.
  • Avoid being in close contact with others who are sick.
  • Cover your mouth with a tissue or your elbow when you cough or sneeze, and then wash your hands.
  • Regularly clean and disinfect commonly touched surfaces, such as counters, light switches or doorknobs. This can help to prevent spread of infection from touching a surface with the virus on it and then your face.
  • Practice good health habits. Get regular exercise, get enough sleep, drink plenty of fluids, eat a healthy diet, and manage your stress.

If you become sick with the flu, you can also help prevent the spread of the flu by staying home and away from others. Continue staying home until your fever has been gone for at least 24 hours.

During the COVID-19 pandemic, both COVID-19 and the flu may be spreading at the same time. Your local health department and the CDC may suggest additional precautions to reduce your risk of COVID-19 or the flu, such as practicing social distancing and keeping 6 feet (2 meters) away from anyone outside your household. You also may need to wear a cloth face mask when in public, especially when it's hard to maintain distance.

Getting your flu vaccine can reduce your risk of the flu and its complications, and following these precautions can help protect you from the flu or other respiratory illnesses.

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Oct. 15, 2020 See more In-depth