A香港ウイルスの侵入によるインフルエンザの初期疫学像に関する研究

抄録

In July 1968, an epidemic of influenza occurred in Hong Kong, and in August, the pathogenic virus isolated on this occasion, a type A/Hong Kong influenza virus, was clarified to be possessing an entirely different antigenic structure when compared with the conventional type A₂ virus. Scarcely any antibody to it was reported being possessed by any generation opulation except for part of subjects who were more than 70 years old. During the past years, the A type virus has occurred in cycles of about 10 years with various antigenic variations. In order to elucidate the initial epidemiological picture induced by an invasion of this new influenza virus, any work should be completed within 1-2 years after invasion because of the rapidity of propagation of the Influenza virus. In the current Hong Kong A virus epidemics, the author studied several problems concerned with the initial picture of the epidemic. As a result, the Hong Kong strain was isolated from 7 cases in August 1968 and 6 cases in September 1968 in Japan from subjects who had just arrived from epidemic sites in Southeast Asia. The actual epidemic in Japan probably started in Ryogoku Middle School in the first part of October 1968. Towards the end of October, the epidemic continued in the Tokyo-Yokohama and Kyoto-Osaka-Kobe districts, indicating the complete seeding of Hong Kong flu in Japan. The epidemic spread all over the country after January and a peak involving 80% of the cases was seen in February, 1969. This epidemic had a very slow rate of propagation as compared with the Influenza, Asia type. The factors of "an abnormally warm winter" during 1968-1969, differences in the stage of invasion of both epidemics, and differences in the states of vaccination should be taken into consideration. In view of the distribution of antibody titer by serological testing, the stages of epidemics of A and B types was different in 5 of the 9 groups surveyed. No epidemics of both types were noted in the same stage. The fact that the epidemics were always seen in January and February despite vaccine immunization containing type B virus in all the 5 groups and epidemics of both types were noted might indicate a problem in the storage life of the commercial vaccine. Concerning the scope of the epidemics, on the other hand, the author studied the relationship between school epidemics and area epidemics, and established the fact that the epidemics in school groups represented the current state of the regional epidemics.