Influenza outbreaks in Japan in 1951-1953.

As reported previously, the influenza epidemic in 1950-51 was almost over in the end of January, 1951. After that time, there was no influenza epidemic announced in any place of Japan, but sporadic suspected cases with cold-like symptoms, of course, were from time to time found as in usual years , but it was very doubtful that they were really due to influenza virus, indeed we examined some of them but did not succeed to isolate a virus and serological diagnosis was all negative. The same situation lasted until the end of 1951, and no sign of sporadic or localized outbreak of influenza was announced. The year turned. By the end of February, 1952, we heard no case of influenza, and we really knew that in Tokyo area, there were no topics about influenza among people. In the first decade of March, 1952, an outbreak of influenza was reported to us from the Tokyo Police School. Serological diagnosis was made as influenza B and a virus isolated was investigated for its antigenic structures as mentioned below . Though morbidity was considerably high in this outbreak, the epidemic was fortunately strictly confined to the school only. According to the survey, influenza cases had been found already in February among the students and the epidemic lasted until approximately the end of March. Peculiar fact was that a considerable part of the students graduated from school and were dispatched to each place where each of them was destined to take his place, when the epidemic was still raging, and in spite of this fact, there was no sign of spread of influenza in the areas which received those students as policemen. In Tokyo also, there was no epidemic even near, but outside the Police School. Beside the outbreak of the Police School, there was no influenza reported in Tokyo Area, and the winter thus was over. Later Dr. Y. Okuno wrote to us that a considerable number of influenza cases were seen in Osaka Area in the