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The risk of getting the flu after taking the flu shot is low. Studies from previous years show that the flu vaccine, whether given as a shot or nasal spray, appears to protect about 7 out of 10 people from getting sick. The effectiveness of the vaccine during any given flu season depends on the health of the person who receives it and how well-matched the viruses in the vaccine are to the particular viruses circulating at the time.
People whose immune systems are compromised and elderly people are most likely to contract the flu, even if they've been vaccinated, according to the Centers for Disease Control and Prevention. The vaccine itself does not cause the flu.
You cannot get the flu, or influenza, from the flu shot. However, you can still get the flu if you are exposed before protection starts.
After getting the flu shot, your body needs around two weeks to create an immune response capable of fighting off the flu. If you get the flu shot and then get exposed to the flu virus a week later, you may not have the full protection that the flu shot would have given you the next week.
In addition, the flu shot only offers protection against the three most common flu types of the season. If you are exposed to another type of the flu, you will not have protection. Because of this, it is important to get your flu shot every flu season in order to get protection from the flu types of that particular season.
Yes. It’s possible to get sick with the flu even if you have been vaccinated -- although you won’t know for sure unless you get a flu test. Here are some reasons why:
- You may be exposed to a flu virus shortly before getting vaccinated or during the period that it takes the body to gain protection after getting vaccinated. So, you may get sick before the vaccine begins to protect you. It takes about two weeks after vaccination for you to develop the antibodies that provide protection against the flu.
- You may be exposed to a flu virus that is not included in the seasonal flu vaccine. There are many different flu viruses that spread every year. The flu vaccine is made to protect against the three or four flu viruses that research suggests will be most common.
- Some people get the flu even though they get vaccinated. Protection provided by flu vaccination can vary widely, based in part on the health and age of the person getting vaccinated. In general, the flu vaccine works best among healthy younger adults and older children. Some older people and people with certain chronic illnesses may develop less immunity after vaccination. Flu vaccination is not a perfect tool, but it is the best way to protect against flu infection.
For everyone, getting vaccinated each year provides the best protection against influenza throughout flu season. It’s important to get a flu vaccine every season, even if you got vaccinated the season before and the viruses in the vaccine have not changed for the current season. The presence of the CDC logo and CDC content on this page should not be construed to imply endorsement by the US Government of any commercial products or services, or to replace the advice of a medical professional. The mark “CDC” is licensed under authority of the PHS.
You can still get the flu, even if you got a flu vaccine. The flu shot lowers your chances of getting influenza, and if you do get the flu, it's likely to be less severe.
There are over a hundred strains of influenza. The shot usually protects against the top three or four strains, so there are a number of strains not covered. However, some of these strains are close enough that the flu vaccine will still offer some protection. Sometimes, the predictions are wrong, and the wrong strains are in the flu shot for that particular year. In addition, not everyone who gets the shot will be immunized. These people are called non-responders. This changes from year to year, but around 90 percent of people will respond to the shot, so there are some people who even though they got the shot are not protected.
You can still get the flu if you've had a flu shot because it will not provide 100% protection against the flu. The flu vaccine is not foolproof. When the vaccine and the circulating viruses are similar, the vaccine can prevent the flu among 70% to 90% of healthy adults under 65. Even if you do get the flu, the vaccine can still protect you against flu-related complications by minimizing the severity of the illness. And, contrary to flu myths out there, you cannot get the flu from a flu shot or the nasal vaccine.
This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.