Rickettsia tsutsugamushi strains from three recent patients of Tsutsugamushi disease in Niigata Prefecture were isolated primarily in mice and then in L cell cultures. By this procedure, low virulent strains to mice, as well as high virulent ones, could be isolated and cultivated serially in L cell cultures, suggesting the usefulness of L cells for isolation of this species of rickettsia. Each newly isolated strain was identified as a member of R. tsutsugamushi from the results of cross immunological tests and morphological observation. On the other hand, it was recognized that one of these rickettsiae showed immunological properties distinguishable from the prototype strains of Kato, Karp, and Gilliam by the cross complement fixation test, and also had low virulence in mice.

The reactogenicity and immunogenicity of Tween-ether split trivalent A(H1N1), A (H3N2), and B influenza vaccine in primary school children aged seven to 12 years, and the persistence of antibodies following two doses of vaccine were studied during 1980-1984. Adverse reactions were infrequent, and, even when reported, were chiefly local ones, mild in nature and of short duration. Most of the reactions were less frequent after the second dose than after the first dose. Most of the systemic reactions occurred during the intervaccination period with almost equal frequency, indicating that careful consideration is required to judge whether they were induced by vaccination or not. This vaccine had induced adequate hemagglutination inhibiting (HAI) antibody because the geometric mean titers (GMTs) of the vaccinees were two-to eightfold higher than those of the nonvaccinees to any of the vaccine antigens following two doses of vaccine. In general, the responses to A(H3N2) virus were the best among the vaccine antigens through the four vaccination seasons, but there was a tendency to show a poorer response to the same type (or subtype) of virus antigen as the causative one during a protracted epidemic. The antibodies induced by either vaccination or natural infection were shown to persist for less than a year, supporting the recommendation for annual vaccination.

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