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Current Trends Antigenic Analysis of Recent Influenza Virus Isolates

Most influenza virus isolates recovered in the United States and Europe during the winter of 1982-1983 have been type A(H3N2) strains closely related to A/Bangkok/1/79. This was consistent with increased activity of such strains in the Southern Hemisphere and several tropical Asian countries during July and August 1982 (1). Type A(H3N2) influenza strains continued to be isolated in Asia during late 1982 and early 1983, with sporadic cases in Hong Kong (September), localized outbreaks or moderate epidemics in Japan (February), Korea (December), Pakistan (January), People's Republic of China (December), Taiwan, Province of China (January), Singapore (October), and Thailand (October).

Antigenic analysis of isolates from some Asian countries identified a trend toward a predominance of strains, which, in hemagglutination inhibition (HI) tests with ferret antiserum, differ from A/Bangkok/1/79 or other recent variants. Such strains, called A/Philippines/2/82, were named for the prototype of a series of strains first identified during an outbreak in the Philippines in summer 1982. As shown in Table 1, although antiserum to A/Philippines/2/82 reacts as strongly with A/Bangkok/1/79 as with its homologous antigen, A/Philippines/2/82 antigen is poorly inhibited by the A/Bangkok/1/79 serum.

Antigenic analysis of influenza viruses from Europe and North America examined during the 1982-1983 winter has confirmed the presence of A/Philippines/2/82 virus in these regions, although the predominant strains have been well inhibited by A/Bangkok/1/79 serum. By February, up to 20% of isolates in the United Kingdom were identified as similar to A/Philippines/2/82 in HI tests with ferret antiserum, although Philippines-like strains had been absent earlier in the season. They have also been identified in Belgium, Czechoslovakia, Italy, and the Netherlands. In North America, A/Philippines/2/82-like strains were first isolated in Florida and Manitoba, Canada, in January 1983, and, as of April, had been identified in Connecticut, Georgia, Missouri, New Mexico, New York, Ohio, and Oklahoma. Other H3N2 variants, such as A/Texas/1/77-like strains, A/Bangkok/2/79-like strains, and A/Shanghai/31/80-like strains (Table 1), have also been identified among recent isolates from Asia, Europe and North America.

Antigenic analysis of influenza A(H1N1) and influenza B strains isolated in recent months continues to show their close similarity to A/England/333/80 and B/Singapore/222/79 strains that have circulated in the preceeding recent influenza seasons. Reported by Virus Disease Unit, World Health Organization, Geneva; WHO Collaborating Center for Influenza, Influenza Br, Div of Viral Diseases, Center for Infectious Diseases, CDC.

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