An egg allergy means that your body doesn't accurately identify the proteins in eggs. Instead of recognizing that they're harmless, your immune system flags those proteins as harmful. Whenever you ingest the allergenic egg proteins, your body releases an antibody called immunoglobulin E to fight them off. In turn, it triggers an army of chemicals to wage war against the invading proteins. You suffer allergic symptoms because of the battle going on between the allergens and the chemicals -- particularly because of the histamine that's released.
The reason that some people with egg allergies can't get flu shots is because flu shots contain eggs -- and therefore egg proteins. Still, many people who are allergic to eggs can get flu vaccines under the right conditions. First and foremost, your doctor needs to know about your allergy and how severe it is. If your allergy hasn't been diagnosed by an allergist yet, your physician will probably send you for a skin test to verify that you definitely have an egg allergy. Sometimes, the allergist will also test to see if you're allergic to the flu shot. Once your allergy is determined, the doctor will give you the flu shot but you'll have you stay in the office for at least a half-hour to make sure you don't have any reactions; if you do, you'll have immediate medical attention.
Some doctors do their own version of a flu shot-allergy test. First, they administer 10 percent of the shot and then wait to see if you react. If you don't, you'll get the other 90 percent. If you turn out to be one of the highly allergic people who can't handle a flu shot, your best recourse is to wait and see if you get the flu. If you do, there are flu medications that you can take within the first 24 hours of contracting th flu to alleviate the symptoms and stop it from getting worse.