Getting a flu shot will often protect 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 four of the influenza viruses expected to be in circulation this flu season. High-dose flu vaccines will be available for adults age 65 and older, but these may not be available at all medical centers.
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:
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.
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.
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
- People with weakened immune systems
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:
- Cancer or cancer treatment
- Chronic obstructive pulmonary disease (COPD)
- Heart disease
- Cystic fibrosis
- Brain or nervous system conditions
- Kidney or liver disease
Anyone with a chronic medical condition should get the flu vaccine. Also, people living in nursing homes or other long-term care facilities 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.
The flu vaccine will be available as an injection or as a nasal spray.
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.
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.
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 prevent 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 decrease the number of people needing to stay in the hospital.
It also may be possible to get a COVID-19 vaccine at the same time as your flu vaccine.
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 the 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.
Both COVID-19 and the flu may be spreading at the same time. Your local health department and the CDC may suggest other precautions to reduce your risk of COVID-19 or the flu if you haven't been fully vaccinated. For example, you may need to practice social distancing (physical distancing) and stay at least 6 feet (2 meters) from others outside your household. You may also need to wear a cloth face mask when around people outside your household when indoors and when outdoors in crowded areas. If you're fully vaccinated and are in an area with a high number of new COVID-19 cases in the last week, the CDC also recommends wearing a mask indoors in public and outdoors in crowded areas or when you're in close contact with unvaccinated people.
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.
Sept. 10, 2021
- Bope ET, et al. The infectious diseases. In: Conn's Current Therapy 2018. Philadelphia, Pa.: Elsevier; 2018. https://www.clinicalkey.com. Accessed July 13, 2018.
- AskMayoExpert. Influenza vaccination. Mayo Clinic. 2020.
- Seasonal flu shot. Centers for Disease Control and Prevention. https://www.cdc.gov/flu/prevent/flushot.htm. Accessed June 2, 2021.
- Zachary KC. Treatment of seasonal influenza in adults. https://www.uptodate.com/contents/search. Accessed July 13, 2018.
- Vaccine effectiveness & How well does the flu vaccine work? Centers for Disease Control and Prevention. https://www.cdc.gov/flu/about/qa/vaccineeffect.htm. Accessed Aug. 3, 2018.
- Live attenuated influenza vaccine [LAIV] (The nasal spray flu vaccine). Centers for Disease Control and Prevention. https://www.cdc.gov/flu/about/qa/nasalspray.htm. Accessed July 13, 2018.
- Prevent seasonal flu. Centers for Disease Control and Prevention. https://www.cdc.gov/flu/prevent/index.html. Accessed July 30, 2020.
- Steckelberg JM (expert opinion). Mayo Clinic, Rochester, Minn. Aug. 9, 2018.
- Tosh PK (expert opinion). Mayo Clinic. Aug. 24, 2020.
- How to protect yourself & others. Centers for Disease Control and Prevention. https://www.cdc.gov/coronavirus/2019-ncov/prevent-getting-sick/prevention.html. Accessed Aug. 26, 2021.
- Frequently asked influenza (flu) questions: 2021-2022 season. Centers for Disease Control and Prevention. https://www.cdc.gov/flu/season/faq-flu-season-2021-2022.htm. Accessed Aug. 16, 2021.
- Grohskopf LA, et al. Prevention and control of seasonal influenza with vaccines: Recommendations of the Advisory Committee on Immunization Practices — United States, 2021-2022 influenza season. MMWR Recommendations and Reports. 2021; doi:10.15585/mmwr.rr7005a1.
- When you've been fully vaccinated. Centers for Disease Control and Prevention. https://www.cdc.gov/coronavirus/2019-ncov/vaccines/fully-vaccinated.html. Accessed Aug. 23, 2021.