Unlike the MMR vaccine, the yellow fever vaccine does contain significant amounts of egg protein (ranging from 2.4 – 4.4 micrograms/ml) and so it is contraindicated in individuals with an egg allergy. For egg-allergic individuals requiring a yellow fever vaccine, a risk-benefit analysis is undertaken in specialist allergy clinics. This may include skin prick and intradermal testing to the vaccine with a 2-step graded challenge or 7-step desensitisation being undertaken where appropriate. Studies of larger cohorts of egg allergic individuals have indicated that reactions to the vaccine appear to be significantly related to positive intradermal tests.