EVALUATION OF SABIN LIVE POLIOVIRUS VACCINE IN JAPAN

V. NEUROVIRULENCE OF VIRUS STRAINS DERIVED FROM VACCINEES AND THEIR CONTACTS

Abstract

Fifteen virus strains, five type 1, three type 2 and seven type 3, recovered from the stool of vaccinees and their contacts were tested for neurovirulence in cynomolgus monkeys. These strains were recovered in field trials with Sabin live oral poliovaccine performed between May and July, 1961, in Japan.
Virus grown in monkey kidney cell cultures at the primary passage was inoculated intracerebrally and intraspinally by the method recommended by Sabin.
About a half of the virus strains were considered to be similar in neurovirulence to the original vaccine as measured by the incidence of paralysis after intracerebral inoculation. However, the majority of the strains showed increase of neurovirulence to certain extent when evaluated by “lesion index ”, a method of inclusive scoring of histologic findings. In this lesion index method, the virus concentration, severity of lesions and route of inoculation are taken into account.
The type 2 strains tended to show no or minimal increase in neurovirulence, and the rest, especially type 3 strains, tended to show greater increases.