Asked by Nancy Unger, Mountain View, California
The day after I got my flu shot this year I got very sick -- not with the flu, but with a heavy cold that lasted for weeks. I assumed the timing was just a coincidence, but this fall so many people that I know had the same experience that I'm wondering: Could a flu shot in any way lead to a heavy cold?
Living Well Expert
Dr. Jennifer Shu
Children's Medical Group
In short, the flu shot cannot lead to a long-lasting cold and here's why: The flu (or influenza) vaccine is given yearly as a shot or nasal spray and contains small particles of the influenza virus strains that are thought to be most common during each particular flu season. The viruses used in the shot are killed (inactivated) or weakened (attenuated) so that they can stimulate the body to produce antibodies and protect against a flu infection without making a person sick.
Because it takes about two weeks after a vaccine for the body to make antibodies to protect against the flu, having cold symptoms right away could mean that a person was exposed to a virus just before or soon after getting the vaccine. People who have been vaccinated can also get sick if they have been exposed to a flu strain that was not included in the vaccine. Finally, vaccines are not always completely effective, especially in people with weakened immune systems, leaving people unprotected from the flu.
As with any vaccine, there may be side effects that can occur. The most common side effects of the flu shot are mild ones lasting one to two days. These include soreness, redness or swelling from the shot; body aches; and a low-grade fever (typically 101 F or less).
The flu vaccine is also available as a nasal spray. This vaccine is made from weakened (attenuated) live viruses which can cause some mild side effects (particularly in the nose) but cannot cause the flu or long-lasting cold symptoms either. The most common side effects can last for a couple of days and include runny nose or congestion, sore throat, cough, headache, and tiredness. Children may also have vomiting, wheezing, muscle aches, or fever. The nasal spray may be given from 2 years to 49 years of age but should not be given during pregnancy or if there are certain long-term medical conditions such as chronic asthma, heart disease, or a weakened immune system; in these cases, the shot should be given instead.
Getting the flu vaccine is the best way to prevent the flu, even if the strains in the vaccine don't exactly match those infecting the community. In this instance, vaccination can still decrease the severity of a flu infection and reduce the risk of serious complications such as pneumonia and the need for hospitalization (particularly in those with weakened immune systems, infants, and elderly people). The flu vaccine should not be given if a person is sick with a fever, is under 6 months of age, has a severe allergy to eggs, or has had a serious reaction to a flu vaccine in the past.
For more information about your specific situation, be sure to talk with your doctor.
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