Effect of Trivalent Oral Poliovirus Vaccine in an Institutionalized Population With Varying Natural and Acquired Immunity to Poliomyelitis

Ninety-one children in an orphanage, who had varying degrees of natural and acquired immunity to polioviruses, were given three doses of a trivalent poliovirus vaccine at monthly intervals. It was found that among children who lacked protection to one or two types, a single dose of trivalent vaccine resulted in seroconversion to that type. For those who had antibody levels of less than four to all three types, the type 1 component of the vaccine appeared to be less effective than the other two types. An elevation in serum antibody titer was noted more frequently in children who had preimmunization titers of 1:64 or less than in those with high preimmunization titers. Although the mechanism of acquisition of prior immunity was unknown, it must be assumed that many of the subjects had had natural poliovirus infection in the past.