ANALYSIS OF INFLUENZA-A H3N2 STRAINS ISOLATED IN ENGLAND DURING 1995-1996 USING POLYMERASE CHAIN-REACTION RESTRICTION

A polymerase chain reaction-restriction (PCR-restriction) endonuclease assay was developed to allow rapid analysis of influenza A H3N2 virus es circulating in England during 1995-1996. Restriction endonuclease d igestion with two enzymes of amplicons derived from PCR of the HA1 por tion of the influenza haemagglutinin (HA) gene was able to differentia te antigenically similar influenza strains into two groups. Group I va riants were similar genetically to the 1995/96 vaccine strain, A/Johan nesburg/33/94, whereas the HA sequences of Group II variants were simi lar genetically to the reference virus A/Thessa-loniki/1/95. Of the 70 0 England A H3N2 strains isolated between February 1995 and the end of April 1996, 384 were analysed by this method. PCR-restriction analysi s of sequential influenza isolates revealed a temporal alteration in p revalence of the two va ria nts. Groups I and II va ria nts cocirculat ed with equal frequency during a period of sporadic influenza activity , but following the onset of epidemic influenza activity in 1995, only Group II variants were detected. PCR- restriction analysis was found to be a rapid method for studying genetic variation which could be app lied to a large number of samples and provide information about the di rection of genetic drift in the HA gene of influenza virus. (C) 1997 W iley-Liss, Inc.