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Flu Shot Facts and Myths
Posted on Oct 8th, 2019
Reprinted from CDC cdc.gov
Misconceptions about Flu Vaccines
Can a flu vaccine give you the flu?
No, flu vaccines cannot cause flu illness. Flu vaccines given with a needle (i.e., flu shots) are currently made in two ways: the vaccine is made either with a) flu viruses that have been ‘inactivated’ (killed) and that therefore are not infectious, or b) using only a single gene from a flu virus (as opposed to the full virus) in order to produce an immune response without causing infection. This is the case for recombinant influenza vaccines.
Are any of the available flu vaccines recommended over the others?
CDC recommends use of any licensed, age-appropriate influenza vaccine (inactivated influenza vaccines [IIV], recombinant influenza vaccine [RIV], or live attenuated influenza vaccine [LAIV4]) with no preference expressed for one vaccine over another during the 2018-2019 flu season. Nasal spray vaccine (LAIV4) is again a recommended option for people for whom it is otherwise appropriate. Different flu vaccines are approved for use in different groups of people. Factors that can determine a person’s suitability for vaccination, or vaccination with a particular vaccine, include a person’s age, health (current and past) and any allergies to flu vaccine or its components.
Unlike the flu shot, the nasal spray flu vaccine (also known as the “live attenuated influenza vaccine” or “LAIV”) does contain live influenza viruses, but the viruses are attenuated (weakened), so that they will not cause flu illness. In addition, these weakened viruses are cold-adapted, which means they are designed to only replicate (multiply) at the cooler temperatures found within the nose. These viruses cannot infect the lungs or other areas where warmer temperatures exist.
Is it better to get the flu than the flu vaccine?
No. Flu can be a serious disease, particularly among young children, older adults, and people with certain chronic health conditions, such as asthma, heart disease or 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.
Do I really need a flu vaccine every year?
Yes. CDC recommends a yearly flu vaccine for just about everyone 6 months and older, even when the viruses the vaccine protects against have not 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 against the flu.
Why do some people not feel well after getting the seasonal flu vaccine?
Some people report having mild reactions to flu vaccination. The most common side effects from flu shots are soreness, redness, tenderness or swelling where the shot was given. Low-grade fever, headache and muscle aches also may occur. If these reactions occur, they usually begin soon after the shot and last 1-2 days. In randomized, blinded studies, where some people get inactivated flu shots and others get salt-water shots, the only differences in symptoms was increased soreness in the arm and redness at the injection site among people who got the flu shot. There were no differences in terms of body aches, fever, cough, runny nose or sore throat.
Side effects from the nasal spray flu vaccine may include: runny nose, wheezing, headache, vomiting, muscle aches, fever, sore throat and cough. If these problems occur, they usually begin soon after vaccination and are mild and short-lived. The most common reactions people have to flu vaccines are considerably less severe than the symptoms caused by actual flu illness.
What about serious reactions to flu vaccine?
Serious allergic reactions to flu vaccines are very rare. If they do occur, it is usually within a few minutes to a few hours after the vaccination. While these reactions can be life-threatening, effective treatments are available.
What about people who get a seasonal flu vaccine and still get sick with flu symptoms?
There are several reasons why someone might get a flu symptoms, even after they have been vaccinated against flu.
Can vaccinating someone twice provide added immunity?
In adults, studies have not shown a benefit from getting more than one dose of vaccine during the same influenza season, even among elderly persons with weakened immune systems. Except for some children, only one dose of flu vaccine is recommended each season.
Is it true that getting a flu vaccine can make you more susceptible to other respiratory viruses?
There was one study (published in 2012) that suggested that influenza vaccination might make people more susceptible to other respiratory infections. After that study was published, many experts looked into this issue further and conducted additional studies to see if the findings could be replicated. No other studies have found this effect. For example, this article [99 KB, 5 pages] in Clinical Infectious Diseases (published in 2013). It’s not clear why this finding was detected in the one study, but the preponderance of evidence suggests that this is not a common or regular occurrence and that influenza vaccination does not, in fact, make people more susceptible to other respiratory infections.
Misconceptions about Flu Vaccine Effectiveness
Influenza vaccine effectiveness (VE) can vary from year to year, by virus type and subtype, and among different age and risk groups. For more information about vaccine effectiveness, visit How Well Does the Seasonal Flu Vaccine Work)?
There are many reasons to get a flu vaccine each year. Below is a summary of the benefits of flu vaccination, and selected scientific studies that support these benefits.
*References for the studies listed above can be found at Publications on Influenza Vaccine Benefits.
Misconceptions about the Timing of Seasonal Influenza Vaccination
Should I wait to get vaccinated so that my immunity lasts through the end of the season?
CDC recommends that people get a flu vaccine by the end of October. Getting vaccinated later, however, can still be beneficial. As long as flu viruses are circulating, it is not too late to get vaccinated, even in January or later. While seasonal flu outbreaks can happen as early as October, most of the time flu activity peaks between December and February, although activity can last as late as May. Since it takes about two weeks after vaccination for antibodies to develop in the body that protect against flu virus infection, it is best that people get vaccinated in time to be protected before flu viruses begin spreading in their community.
How long you are immune or your “duration of immunity” is discussed in the ACIP recommendations. While delaying getting of vaccine until later in the fall may lead to higher levels of immunity during winter months, this should be balanced against possible risks, such as missed opportunities to receive vaccine and difficulties associated with vaccinating a large number of people within a shorter time period.
Is it too late to get vaccinated after Thanksgiving (or the end of November)?
No. Vaccination can still be beneficial as long as flu viruses are circulating. If you have not been vaccinated by Thanksgiving (or the end of November), it can still be protective to get vaccinated in December or later. Flu is unpredictable and seasons can vary. Seasonal flu disease usually peaks between December and March most years, but disease can occur as late as May.
Misconceptions about Physician Consent for Vaccination
Do pregnant women or people with pre-existing medical conditions need special permission or written consent from their doctor to receive the flu vaccine?
No. There is no recommendation for pregnant women or people with pre-existing medical conditions to seek special permission or secure written consent from their doctor for vaccination if they get vaccinated at a worksite clinic, pharmacy or other location outside of their physician’s office. With rare exception, CDC recommends an annual flu vaccine for everyone 6 months and older, including pregnant women and people with medical conditions.
A variety of flu vaccine products are available (Table 1). Vaccine providers should be aware of the approved age indications of the vaccine they are using and of any contraindications or precautions. Providers also should appropriately screen all people getting vaccinated for allergies to vaccine components or other contraindications. People who have previously had a severe allergic reaction to influenza vaccine or any of its ingredients should generally not be vaccinated.
There are some people who should not get a flu vaccine without first speaking with their doctor. These include:
Pregnant women or people with pre-existing medical conditions who get vaccinated should get the flu shot.
If a person is vaccinated by someone other than their primary health care provider, the vaccinating provider should ensure that the patient and, if possible, the patient’s medical provider have documentation of vaccination.
For a complete list of people who should not get the vaccine before speaking with their doctor, please review the influenza Vaccine Information Statement for the flu shot.
Misconceptions about “Stomach Flu”
Is the “stomach flu” really the flu?
No. 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. 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 symptoms of influenza. The flu is a respiratory disease and not a stomach or intestinal disease.