Misconceptions about Flu and the Flu Vaccine

Author: Centers for Disease Control and Prevention (CDC)

Hello. I'm Dr. Joe Bresee with CDC's Influenza Division.

This video is intended for general audiences, as well as physicians and other healthcare providers. Today, I'll provide answers to several common questions and misconceptions patients have regarding the flu and the flu vaccine. I'd like to begin by addressing a common misconception about flu illness -- the belief that flu is not a serious disease.

Truth is, flu is, in fact, a serious disease that causes illness, hospitalizations, and deaths every year in the U.S. Even healthy children and adults can get very sick from the flu and spread it to family and friends. CDC estimates that each year on average, 5% to 20% of the U.S. Population are infected with the flu. In addition, CDC estimates that more than 200,000 people may be hospitalized each year because of the flu. Flu-related deaths vary but are significant. Over a period of 30 years, between 1976 and 2006, estimates of yearly flu-associated deaths in the U.S.

Range from a low of about 3,000 to a high of about 49,000. People also have misconceptions about the kinds of illness associated with the flu. You've likely heard someone say they have the stomach flu. And so I think it's important to answer the question, is the stomach flu the same as the flu? The answer is no.

Misconceptions about Flu and the Flu Vaccine

Many people use the term "stomach flu" to describe illnesses with nausea, vomiting, or diarrhea. These symptoms can be caused by many different viruses, bacteria, or even parasites. I'd like to emphasize that the flu is a respiratory disease and not a stomach or intestinal disease. While vomiting, diarrhea, and being nauseous or sick to your stomach can sometimes be related to the flu more commonly in children than adults, these problems are rarely the main symptom of flu. The most common flu symptoms are fever or feeling feverish with chills, cough, sore throat, runny nose or stuffy nose, muscle or body aches, headache, fatigue, or feeling tired. As previously stated, some people may have vomiting and diarrhea. It's also worth mentioning that not everyone who has the flu will have a fever.

Now that we've covered a few misconceptions about flu illness, I'd like to move on to discuss misconceptions about the flu vaccine. I'll begin with a common question. Can a flu shot give you the flu? The answer is no.

A flu shot cannot cause flu illness. The influenza virus is contained in the flu shot or inactivated -- in other words, killed -- which means they cannot cause infection. People also commonly ask about the nasal spray flu vaccine and whether it can cause flu illness. Unlike the flu shot, the nasal spray vaccine does contain live viruses. However, the viruses contained in the nasal spray flu vaccine are attenuated -- in other words, weakened -- which means they cannot cause flu illness either. These weakened viruses are also cold-adapted, which means they're designed to only cause mild infection at the cooler temperatures found within the nose. These viruses cannot infect the lungs or other areas of the body where warmer temperatures exist.

So, let's move on to a different but related question. Why do some people not feel well after getting the flu vaccine? It's true that some people report having mild reactions to flu vaccination. I would like to begin by talking about flu shots. The most common reaction to the flu shot in adults has been soreness, redness, or swelling at the spot where the shot was given. This usually lasts less than two days. This initial soreness is most likely the result of the body's early immune response reacting to a foreign substance entering the body.

Other reactions following the flu shot are usually mild and can include low-grade fever and aches. If these reactions occur, they usually begin soon after the shot and last one to two days. I'd like to emphasize that the most common reactions people have to flu vaccines are considerably less severe than the symptoms caused by actual flu illness.

People also may have mild reactions to the nasal spray vaccine. In children, reactions to the nasal spray vaccine can include a runny nose, wheezing, headache, vomiting, muscle aches, and fever. In adults, reactions to the nasal spray vaccine can include a runny nose, headache, sore throat, and cough. Serious allergic reactions to flu vaccines are very rare.

If they do occur, it's usually within a few minutes to a few hours after the vaccination. While these reactions can be life-threatening, effective treatments are available. The next question asks, what about people who get a flu vaccine and still get sick with flu-like symptoms? There are several reasons why someone might get a flu-like illness even after they've been vaccinated. One reason is that some people can become ill from other respiratory viruses besides flu, such as rhinoviruses, which are associated with the common cold, that circulate during the flu season and also cause flu-like symptoms. Remember flu vaccine only protects against flu viruses, not other viruses.

Another explanation is that it's possible to be exposed to influenza viruses, which cause the flu, shortly before getting vaccinated or during the two-week period after vaccination that it takes the body to develop immune protection. This exposure may result in a person becoming ill with the flu before protection from the vaccine takes effect. A third reason why some people may experience flu-like symptoms despite getting vaccinated is that they may have been exposed to an influenza virus that is very different from the viruses the vaccine is designed to protect against. The ability of a flu vaccine to protect a person depends largely on the similarity or match between the viruses selected to make the vaccine and those spreading and causing illness in the community. There are many different influenza viruses that spread and cause illness among people.

For more information, visit the URL featured in this presentation. The final explanation for experiencing flu-like symptoms after vaccination is that, unfortunately, the flu vaccine is not 100% effective, and sometimes it doesn't provide adequate protection against the flu. This is more likely to occur among people that have weakened immune systems or people 65 years and older. However, even among those of people, a flu vaccine can still help prevent flu-related complication. The next question is, is it better to get the flu than the flu vaccine? Short answer is no. We discussed earlier that the flu is a serious disease, particularly among young children, older adults, and people with certain chronic health conditions such as asthma, heart disease, and diabetes. Any flu infection can carry a risk of serious complications, hospitalization, or death, even among otherwise healthy children and adults. Therefore, getting vaccinated is a safer choice than risking illness to obtain immune protection.

The next question is, do I really need to get a flu vaccine every year? The answer is yes. CDC recommends a yearly flu vaccine for just about everyone six months and older, even when the viruses the vaccine protects against haven't changed from the previous season. The reason for this is that a person's immune protection from vaccination declines over time, so an annual vaccination is needed to get the optimal or best protection you can get against the flu. The next question addresses the timing of vaccination. The question is, should I wait to get vaccinated so that my immunity lasts through the end of the season? The answer to this question is no. CDC recommends that influenza vaccination begin as soon as the flu vaccine becomes available in your community and continue throughout the flu season. The flu season is unpredictable, and since it takes about two weeks after vaccination for antibodies to develop in the body that protect against influence virus infection, it's best that people get vaccinated early so they're protected before influenza begins spreading in their community.

While immunity can vary by person, previously published studies suggest that immunity lasts through a full flu season. Although adults 65 and older typically have a reduced immune response to flu vaccination compared with young, healthy adults, their immune protection still extends through one flu season. In addition, a review of published studies concluded that no clear evidence exists that immunity declines more rapidly in the elderly. It's worth noting that the new high-dose vaccine for people aged 65 and older is intended to create a stronger immune response in this age group. The next question also deals with vaccine timing. The question is, is it too late to get vaccinated after Thanksgiving? The answer is no. Vaccination can still be beneficial as long as influenza viruses are circulating. Flu season most often peaks in January or February and can last as late as May in the United States.

And now for the last question. Can vaccinating someone twice during an influenza season provide added immunity? The only group of people recommended to receive more than one flu vaccine during a single season are children 6 months through 8 years of age who are receiving the vaccine for the first time. These children need to get two doses of flu vaccine four or more weeks apart during the first season of vaccination to be fully protected. The first dose primes the immune system, and the second dose provides immune protection.

Children who only get one dose but need two doses can have reduced or no protection from a single dose of flu vaccine. For all other groups, studies have not demonstrated a benefit from receiving more than one dose of flu vaccine during an influenza season, even among older people with weakened immune systems. This concludes the CDC video on answers to common questions and misconceptions about the flu and the flu vaccine. Thank you for watching. For more information related to the flu and the flu vaccine, please visit the CDC flu webpage at www.cdc.gov/flu.

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