vaccinal prophylaxis against poliomyelitis , carried out regularly in the ussr for many years , has erected a reliable barrier to the epidemic manifestation of this disease in large areas of the ussr over the period of almost 25 years ( the term of observation ) and introduced new features into its epidemiology : the sluggish course of the epidemic process , a decrease in the relative morbidity rate in cities , a lower morbidity rate among children attending preschool institutions , the absence of the family foci of poliomyelitis , more favorable outcome oft the disease .
C0032374
vaccinal
C0032371
poliomyelitis