Clinical and epidemiological features of an outbreak of influenza in Ulan Bator in 1971.

In October and November 1971 an outbreak of influenza (type A virus) occurred in the town of Ulan Bator. A clinical and epidemiological investigation showed that some 30% of the population presented typical signs of influenza of medium severity. The etiology of the outbreak was confirmed by virological, serological, and fluorescent-antibody techniques. A detailed study of the antigenic structure of the virus isolated in the Mongolian People's Republic, A/Mongolia/013/71, showed that it belonged to a new antigenic variety of the Hong Kong strain, A/Hong Kong/107/71 (H3N2).