Because viruses are obligate intracellular parasites, vaccines against viruses must be produced using human or animal cells. Influenza vaccines currently used in Canada are produced by allowing the virus to multiply in chicken egg embryos. Despite rigorous purification processes, these vaccines, including Flumist®, still contain low residual quantities of ovalbumin (egg protein). The quantity of residual ovalbumin differs, at times significantly, between the different commercial influenza vaccines available in Canada, but also between different lots of the same vaccine [3]. While manufacturers have to assure that the influenza vaccines destined for the Canadian market do not contain more than 0.24 µg/dose of residual ovalbumin[ ], they are not required to divulge the final quantity. For this reason, a theoretical risk of anaphylaxis or hypersensitivity still exists in egg-allergic patients. However, the real risk of an anaphylactic reaction after an intramuscular influenza vaccination in an egg-allergic patent is quite low[1].