POLYMORPHISM OF MODERN INFLUENZA-A AND IN FLUENZA-B VIRUS POPULATION

During the past years, the etiological situation has been significantl y complicated. It is characterized by simultaneous circulation of A (H 1N1), A(H3N2) and influenza B viruses and by the isolation of reassort ant strains and viruses, which are atypical in relation to the process of their natural variability. The antigenic properties of epidemic st rains and unusual isolates were investigated. The marked heterogeneity of the A(H3N2) influenza viruses was demonstrated. It was determined by the circulation of several antigenic variants during the epidemic. Two separate antigenic lineage of the influenza B viruses - b/Victoria /2/87 and B/Yamagata/16/88 - cocirculated in our country in 1991. Sinc e 1986, all the influenza A(H1N1) viruses have been considered to be v arieties of the reference strain A/Taiwan/1/86. A direct correlation w as found between some atypical viruses and the vaccine strains previou sly used.