Mass Immunization of Children With Oral, Trivalent Poliovirus Vaccine (Lederle Strains)

A campaign against poliomyelitis in Bogota, Colombia, utilizing an orally administered trivalent poliovirus vaccine (Lederle strains) demonstrated its particular value in public health campaigns, as well as its effectiveness and safety. A single dose of vaccine, administered to more than 187,000 children under 7 years of age within a 2-month period by personnel limited in number and without previous similar experience, greatly reduced both the number of children susceptible to poliomyelitis and the incidence of the disease in the community. Estimated reductions in the number of seronegative children among those vaccinated were from 47% to 7% for Type I poliovirus, from 37% to 20% for Type II, and from 46% to 3% for Type III, with even greater reductions in the number of seronegative children under 4 years of age. In addition, the vaccine viruses apparently spread to unvaccinated members of the community with no increase in virulence, resulting in a sharp reduction in the incidence of paralytic poliomyelitis during the following year and in an unprecedented 4-month period without a single case between 7 and 12 months after the mass vaccinations. Although four cases of poliomyelitis occurred among the vaccinated children, all originated at about the time of the vaccination and two of them must have been caused by wild polioviruses or other enteric viruses, which may also have been responsible for the other two cases. In any event these two cases represent only 0.01% of all the children vaccinated.