EVALUATION OF SABIN LIVE POLIOVIRUS VACCINE IN JAPAN

VI. LARGE SCALE USE OF VACCINE DURING TYPE 1 POLIOMYELITIS EPIDEMIC, 1961

Abstract

Sabin type 1 vaccine was given to 292, 316 children, 3 months to 6 years of age, during the polio type 1 epidemic in Japan in 1961. Study areas were selected in Hokkaido, Fukuoka and Kumamoto Prefectures. Of 66, 780, 193, 505, and 121, 235 children in those age groups residing in the study areas, 61.3, 79.8 and 79.8% respectively, were vaccinated. Interpretation of the data was complicated by the fact that these field trials were followed 2 or 3 weeks later by a nationwide mass vaccination with Sabin trivalent vaccine.
No side reactions of any consequence were observed, nor did any parents complain of unusual reactions. A sharp decline in morbidity was observed after vaccination in Fukuoka, Kumamoto and other Prefectures in Kyushu. Of significance is the finding that the delay in the sharp decline corresponded to the delay in the vaccination. This was also the case when the morbidity data in the study areas were compared with those in the remaining areas in Fukuoka and Kumamoto Prefectures. These findings suggest that the vaccination with Sabin vaccine interfered with further progress of the epidemic, although it is possible that this time relationship was merely fortuitous. Because of the nationwide mass vaccination, the morbidity data used for comparison between the vaccinated and unvaccinated children in the study areas had to be limited to those obtained during the period between those two vaccination programs. The morbidity in the vaccinated children was much lower than in the unvaccinated children. Since those two groups of children were comparable regarding the age distribution and various environmental conditions but were not comparable regarding the history of Salk vaccination, a further comparison in morbidity was made after the children were divided by the Salk vaccination history, resulting in confirmation of the above finding. However, it seems difficult to draw a definitive conclusion from those data, because of the limited number of cases.