[The level of herd immunity against poliomyelitis in children during the mass vaccinal prophylaxis of this infection].

The results of examinations of blood sera from normal children for the presence of antibody to polioviruses after two courses of mass vaccinations were carried out according to epidemiological indications although differing in duration of the campaign and the range of the child populations involved, are presented. The advantages of simultaneous mass vaccinations covering children from 2 months to 7 years of age have been demonstrated.