Formaldehyde is a chemical also used in the production of killed vaccines. It’s used very early in the manufacturing process to kill or inactivate the toxins from micro organism or viruses. Formaldehyde may be found naturally in our bloodstream at ranges far greater than we might be exposed to in vaccines. The live nasal spray flu vaccine given to children has a really low egg protein content. Children and adults with a severe egg allergy can safely receive the MMR vaccine.