IN A MASS poliomyelitis vaccination program in Hillsborough County, Florida, almost 200,000 persons were fed trivalent vaccine given in two doses eight weeks apart.1 Among them were 142 children without antibody to any type of poliovirus before vaccination, whose antibody levels one year later were previously reported.2 The antibody levels of 107 of these children exactly two years after their second dose of vaccine are reported here.
Materials and Methods
The 142 children whose one-year antibody status was studied were not selected in any way except that they were those without antibody to any type of poliovirus before vaccination from whom serum specimens could be obtained about a year later. The 107 children reported here are those in the original sample group from whom serum specimens could be obtained the following year. The distributions of their ages and the vaccine lots they and the entire original