Ferret kits need to be vaccinated against distemper at 8 week as well as at 12 and 16 because the immunity that they get to distemper from their mother only last about 6-8 weeks. The immunity only conferred during the first feeding and not the entire time the kits are nursing. If they are not vaccinated until 12 weeks they have about a period of 4-6 weeks when they have no immunity. However, at 8 weeks of age their immune systems are not mature enough to effectively deal with the vaccine and hence two more boosters are required. This explains why an adult with an unknown vaccination record only needs two shots at 3-4 week intervals, while kits need three. So no, it has nothing to do with a hang over from cats and dogs it has to do with how the immune system works. Carolyn McColl Division of Life Sciences Department of Endocrinology and Immunology University of Toronto at Scarborough Scarborough, ON M1C 1A4 [Posted in FML issue 1905]