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It was very surprising for most virologists that two different shift strains, H3N2 and H 1 N 1, caused the pandemic at the same time and in the same place among human beings during the last winter (1977)(1978). Indeed, in most countries, A/USSR/90/77-like strains (H1N1) were isolated simultaneously with A/Texas/ 1 /77-like strains (H3N2) or A/Victoria/3/75-like strains (H3N2) or both (Center for Disease Control, 1978). In addition, Dr. Kendal and his coworkers were successful in isolation of three different influenza A viruses from a high school student in Wyoming, U.S.A. These isolates were characterized and identified as A/ Victoria/ 3 / 75-like strain, A/ USSR/ 90/ 77-like strain and the recombinant strain (H3N1) A similar result involving the Texas and USSR strains was obtained by us.
Yamane et al. (1978) studied this question.