Booster Effect of Oral Poliovaccine: Trials in Persons Previously Immunized With Inactivated Vaccine

EITHER formaldehyde-solution-inactivated poliovaccine (IPV) or live-attenuated poliovaccine (OPV) may be used for poliomyelitis immunization. In the United States OPV is now administered more frequently than IPV. 1 Moreover, many persons previously vaccinated with IPV have now received a complete series of monovalent OPV as secondary immunization. The number of persons under 20 years of age thus vaccinated was estimated from Bureau of Census data to number 30 million in 1965. 1 Several studies have confirmed that single doses of monovalent OPV do provide adequate booster responses in IPV-vaccinated persons. 2-5 Similarly, clinical trials with the newer trivalent vaccines have included assessment of their value as booster agents. A single dose of balanced trivalent OPV has been successfully used to fill immunologic gaps in populations possessing a high degree of natural immunity. 6-8 Two doses of high titer vaccine have yielded a good response in preschool IPV-vaccinated children. 9 However, small