Abstract
Some of the strains influenza B isolated between 1975 to 1978 showed a significant drift away from the prototype strain B/HK/8/73 when tested by cross haemagglutination-inhibition. A serum survey for antibody to two strains of influenza B virus was carried out comparing haemagglutination-inhibition (HI) and single-radial haemolysis (SRH) tests. The SRH technique was found to be more sensitive than the HI test.
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