Are flu vaccines safe for people with egg allergies?

A new study has found that current influenza vaccines contain much smaller amounts of egg protein than previously believed, which would make these injections safe for most adults and children with an egg allergy.

The manufacturing approach for the flu vaccine has changed very little since the 1930s. It involves inoculating the virus in embryonated hens’ eggs, then harvesting and purifying the virus after incubation.

Since there are always some remaining traces of egg protein, this vaccine is not recommended for individuals with a hypersensitivity to eggs (e.g. hives, swelling of the mouth or throat, difficulty breathing). It is estimated that 3.6 percent of people are allergic to eggs. Rare cases of anaphylaxis (severe allergic reaction) have been reported after immunization with the influenza vaccine. New data may lead to a re-evaluation of this recommendation, however.

A new study has found that current influenza vaccines contain much smaller amounts of egg protein than previously believed, which would make these injections safe for most adults and children with an egg allergy.

The higher the level of egg protein in a vaccine, the higher the risk of an allergic reaction. The vaccine is currently recommended for patients with egg allergy only if it’s known to contain no more than 1.2 mcg/mL of egg protein. Vaccine package inserts generally list content ranges much higher than this limit.

However, tests performed on vaccines approved in the United States for the 2010-2011 season showed that all vaccines tested were well below the 1.2-mcg/mL safety mark, with the levels of egg protein ranging from 0.00066 to 0.330 mcg/mL.

Based on this report, doctors are suggesting that persons allergic to eggs could therefore safely get the influenza vaccine. Still, there is a lot of variability among vaccine lots, years of production and manufacturers. Before removing the vaccine restriction for people with egg allergies, however, the concentrations of egg protein in each flu vaccine lot should be verified by regulatory bodies or research institutes.

In order to offset the drawbacks of the long process of producing vaccines in hen’s eggs, researchers are trying to produce these vaccines using cell cultures. For now, though, cultivating the virus in embryonated hens’ eggs remains the preferred method.

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