" " Flu strains are grown inside of eggs before they're deactivated for flu vaccines. So most types of influenza vaccines contain a small amount of egg protein, which may trigger an allergic response from people with egg allergies. When someone with an egg allergy eats an egg, their immune system goes into attack mode against the proteins in the whites and/or yolks of the egg. This decision is based on studies of both the nasal spray vaccine and flu shot in both people with and without egg allergies. Now That's Interesting Egg protein, the protein in influenza vaccines, has the exact mix of essential amino acids humans need to build tissues.