Ask the Doctors: Those allergic to eggs can safely get a flu shot
A: You're smart to ask, especially now. As the current flu season illustrates, the influenza virus accounts for thousands of illnesses and deaths each year. The number of deaths attributed to influenza over the past 40 years has ranged from 3,349 to 56,000 a year; the average annual death rate is about 23,000.
Traditionally, and for the majority of flu shots, the influenza virus is created by injecting it into fertilized chicken eggs, where it multiplies. The fluid within the egg is eventually removed, inactivated and used for the injectable vaccine. Although this fluid is saturated with the virus, it also contains egg protein. That's potentially a problem because many people are allergic to eggs, with up to 2 percent of American children having egg allergies. Some of these allergies manifest as hives, but others are life-threatening, with severe shortness of breath and a rapid decline of blood pressure (called an anaphylactic reaction).
Thus, the primary worry about the use of eggs to make the vaccine has been that the vaccine could lead to major allergic reactions. Four people died of anaphylactic reactions after receiving the influenza vaccine between 1990 and 2005. (Whether these four people had an allergy to eggs is unknown.)
Because of the risk, manufacturers for years have been trying to reduce the amount of egg protein within the vaccine — and they've succeeded. Inactivated flu vaccines are supposed to contain less than 1 microgram of egg protein per dose, but the protein content of vaccines has been measured to be significantly lower than this. Testing of the 2010 and 2011 influenza vaccines, for example, found the level to be 0.17 microgram of egg protein per dose of vaccine.
Multiple studies have assessed the impact of giving the flu vaccine to people with egg allergies; some of the vaccines included up to 0.7 microgram of egg protein per dose given. Overall, these studies identified no anaphylactic reactions. One study did show that, in people with egg allergies, about 1 in 100 people experienced minor allergic reactions, which were treated with an antihistamine. Most notable perhaps is that people with a history of anaphylactic reactions to egg did not have reactions when given the vaccine.
Based on this data, both the Centers for Disease Control and Prevention and the American Academy of Pediatrics have stated that the vaccine can be given to people with egg allergies of any severity. They suggest, however, that to address the theoretical possibility of a severe reaction, people giving the vaccine should have medications and resuscitative equipment on hand.
So, yes, your pharmacist was right: Even if you have egg allergies, the flu vaccine is safe. Personally, I'd like to know the concentration of egg protein in any given vaccine (they're made by various manufacturers), with those with lower concentrations given to people with egg allergies. Perhaps that data will come.
For now, if you have a severe allergy to eggs and can't shake your concern about the flu vaccines produced from eggs, you can choose between two that do not require eggs for production. This is also an option if you've had minor reactions to the flu shot in the past.
Regardless of whether you opt for the traditional vaccine (I would) or choose an alternative, the important thing is to get vaccinated. It will reduce your likelihood of severe illness and death.
Robert Ashley, M.D., is an internist and assistant professor of medicine at the University of California, Los Angeles. Send your questions to firstname.lastname@example.org, or write: Ask the Doctors, c/o Media Relations, UCLA Health, 924 Westwood Blvd., Suite 350, Los Angeles, CA, 90095. Owing to the volume of mail, personal replies cannot be provided.
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