Recommendations concerning the necessity of a fifth injection of Salk vaccine must be based on information available about the immune status of individuals who have received 4 injections of Salk vaccine. The best available method to determine susceptibility that does not involve exposure to the virus is to measure the concentration in the serum of neutralizing antibodies against the 3 types of poliovirus. Further, the antibody response which occurs after a booster injection may give more information than measurement of serum antibodies without antigenic stimulation. This report describes the neutralizing antibody titers in the sera of school-age children before and after a fifth injection of Salk vaccine.
Materials and Methods
One hundred and one normal children living in a Children's Home were selected for a fifth injection of Salk vaccine in May, 1961. The dates of all previous injections of Salk vaccine were known. Three or more years had