Influenza in South-East Asia.

period through subclinical or mild infection occurring sporadically. In order to understand how the virus infection recurs in the temperate epidemic zone, a hypothesis has been presented by Fukumi3 that the virus may survive through infections occurring sporadically in the tropical virus-reservoir zone. Several virological and epidemiological studies have been published on influenza in Thailand7•`9,11,13•`17) which is located in the tropical zone. In South-East Asian countries, a year is divided into three seasons, i.e., hot (March to June), rainy (July to October), and cool (November to February) seasons. In this paper, the outbreak of influenza in Thailand is analyzed in relation to the climatological data and a brief discussion is conducted as regards that of influenza in Manila. Fig. 1-3, shows the monthly distribution of the reported case number of influenza in Thailand from 1975 to 1980. The case number increased every year during the period of June to November, i.e., the rainy season, except the year 1978, in which the increase occurred in February. In each year, the smallest monthly case number is 10 to 29% of