Seroepidemiological study of the circulation of influenza C virus in man

The seroepidemiological study of the circulation of influenza C virus was achieved by testing HI antibodies in human sera collected from healthy subjects in Bucharest belonging to various age groups. The investigations were carried out over a two years period (October 1988--September 1990), using 3 influenza C virus strains: C/Taylor/1233/47, C/USSR/0303/77 and C/Moscow/1/84, the last two being antigenically similar. The analysis of the distribution of HI antibody values against the three influenza C virus strains showed that over October 1988--June 1989 the reported circulating viruses belonged to two distinct antigenic groups, one similar to the prototype C/Taylor/47 strains and the other to C/USSR/and/C/Moscow strains, whilst during the July 1989--September 1990 time interval viruses belonging solely to the C/USSR and C/Moscow antigenic group circulated. Similarly, one should note that circulation of influenza C viruses is not seasonal, it can appear anytime and even several times per year; this accounts for the relatively high and permanent antibody level in the population belonging to all age groups.