[Isolates of poliovirus vaccine and immune response to different doses of oral polio vaccine].

Samples of feces and sera obtained from 3-year-old children were studied to increase the knowledge about the circulations of virus vaccines during the massive campaigns. The use of the oral polio vaccine with schemes of massive campaigns allows the circulation of the virus vaccine 2 months after their completion. The use of continual vaccination schemes makes possible the circulation of the virus vaccine for longer periods of time. Even in populations with a low immunity coverage, epidemic outbreaks of the vaccine-derived virus may appear. The total of poliovirus vaccine isolated in 2-year-old children (11 cases, 11.0 %) and the boosts of neutralizing antibodies (51 cases, 51.0 %), show a contradiction between the verification of the infections caused by isolations of the viruses and the results of boosts. The low percentage of isolations of virus vaccine and the highly significant percentages of of seroconversions or boosts to polio virus, allow to infer the occurrence of silent circulation. The silent circulation self limited to 2 months after concluding the campaign is due, among other causes, to the homologous or not induced response by the primary infection with the first dose of oral polio vaccine and by the secondary infections. The self limitation of the circulation of the polio viruses in massive campaigns constitutes an excellent prevention of the risks represented by the vaccine-derived viruses appearing in vaccinations with continual schemes.