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DEAR MAYO CLINIC: Last year I had an allergic reaction (swollen lips and face, itching around the neck and jawline) after getting the flu shot. Since then I found out I am allergic to thimerosal. Is it safe for me to get the vaccine this year?
ANSWER: It is likely you can find a vaccine that you can take safely. There are influenza vaccines available that do not contain thimerosal. Before you get the vaccine again, make an appointment to see a doctor who specializes in allergies. That specialist can do tests to check your allergies and help you find an influenza vaccine that is safe for you.
Influenza, or the flu, is a viral infection that often causes fever, chills, coughing and headaches. In people who have other diseases or medical conditions, and in healthy people older than 50, the flu can lead to serious illness that may require hospitalization. Each year thousands of people die as a result of complications from the flu.
The best way to help prevent an influenza infection is to get a flu vaccination each year, preferably in early November. The vaccine works by causing your body to produce its own protection, called antibodies, against the flu, and is recommended for infants 6 months and older, all children, and all adults. The vaccine can protect you from influenza viruses, but you need to get it every year because the vaccine’s protective effects only last about a year. It is customized each year to protect against the viruses that are most likely to cause disease at that time.
Some preparations of the flu vaccine do contain thimerosal. Thimerosal is a preservative that helps prevent the growth of bacteria or fungi that could make the vaccine unsafe. At this time, thimerosal is only included in containers that hold more than one dose of the flu vaccine intended to be given as an injection, or a shot. These are called multi-dose vials. Thimerosal is used in multi-dose vials to lower the possibility of contamination of the vaccine once the vial has been opened.
Vials of the flu vaccine that have only one injection dose do not need thimerosal because when they are opened, all of the vaccine is used right away. The form of the flu vaccine given as a nasal spray is always packaged as a single dose so it does not include thimerosal either. Currently, about two-thirds of the flu vaccine in the U.S. does not contain thimerosal, so you should be able to easily find an alternative to the preparations containing that preservative. It would be a good idea to see an allergy specialist first, though, to make sure you do not have any other allergies that could cause a reaction to the flu vaccine. For example, some people with egg allergies may have an allergic response to the vaccine. Also, an allergy specialist can help determine if you are currently sensitive to thimerosal.
Your doctor can do a skin test to check your reaction to the different types of flu vaccine. The test involves scratching a tiny amount of the vaccine on your skin and watching to see if your skin reacts to it. If you do not have a reaction to the skin test, your risk of having a significant allergic reaction to the flu vaccine is low, and it is likely to be safe for you. — James Li, M.D., Ph.D., Allergic Diseases, Mayo Clinic, Rochester, Minn.