Influenza surveillance based on oligonculeotide mapping of RNA of H1N1 viruses prevalent in Japan, 1978-1979.

Influenza H1N1 viruses isolated in Japan in 1978-1979 were compared with A/USSR/92/77 and H1N1 viruses isolated in North and South America in 1978 by oligonucleotide mapping of viral RNA. At least four types of H1N1 viruses, distinguished by oligonucleotide pattern, were involved in influenza outbreaks during 1978-1979 in Japan. The first type was prevalent throughout the country from January to March 1978. The second and third types caused sporadic outbreaks during the 1978-1979 winter. The second type was closely related to an H1N1 strain of 1953, A/Omachi/1/53; the third type appeared to be reintroduced from outside of Japan. The fourth type was prevalent from January 1979 and persisted to September 1979. Its origin was a virus closely related to A/California/45/78 virus, which appeared in the United States in late 1978. The oligonucleotide pattern of A/California/45/78 viral RNA was markedly different from that of other 1977-1978 H1N1 viruses; the major change occurred in the polymerase and nucleoprotein genes.