Vaccination is the most effective way to prevent influenza virus infection and its complications. Since then, the two B lineages have been co-circulating worldwide, with variability in terms of geographic distribution and genomic evolution. However, during the 002 seasons, the Victoria-lineage viruses re-emerged in North America and Europe and spread globally. In the 1990s, Yamagata-like viruses became predominant worldwide, whereas the Victoria lineage was mainly restricted to East Asia.

Originally, influenza B viruses represented a homogenous group but, since the late 1980s, they have evolved into two antigenically and genetically distinct lineages, defined by the reference strains B/Yamagata/16/88 (Yamagata lineage) and B/Victoria/2/87 (Victoria lineage). In the past, influenza B viruses were believed to cause milder illness than influenza A, but several studies have recently demonstrated that infections with influenza A and B are clinically indistinguishable and can cause severe complications in both children and adults. Worldwide, these annual epidemics are estimated to cause about 3вЂ“5 million cases of severe illness and 290,000вЂ“650,000 deaths. Influenza A(H1N1), A(H3N2) and influenza B viruses are responsible for a significant disease burden during seasonal epidemics in humans. An influenza B lineage mismatch with the trivalent vaccine occurred in about two-thirds of cases. We found a continuous co-circulation of both B lineages in the period 2004вЂ“2017, and determined that children were particularly vulnerable to Victoria-lineage influenza B virus infections. This study contributes to the understanding of the circulation of influenza B viruses in Italy. Phylogenetic analysis of the HA1 domain confirmed the co-circulation of both lineages and revealed a mixed circulation of distinct evolutionary viral variants, with different levels of match to the vaccine strains. Considering the seasons when B accounted for >вЂ‰20% of all laboratory-confirmed influenza cases, a mismatch was observed in four out of six seasons. A mismatch between the vaccine and the predominant influenza B lineage occurred in eight out of thirteen influenza seasons under study. A higher proportion of infections with both lineages was detected in children, and there was a declining frequency of B/Victoria detections with age. Overall, viruses of B/Victoria and B/Yamagata lineages caused 53.3 and 46.7% of influenza B infections, respectively. ResultsД¬o-circulation of both B lineages was observed each season, although in different proportions every year. Among them, the lineage of 2465 strains (49%) was retrieved or characterized in this study by a real-time RT-PCR assay and/or sequencing of the hemagglutinin (HA) gene. MethodsДЇrom 2004 to 2017, 26,886 laboratory-confirmed influenza cases were registered in Italy, of which 18.7% were type B. In this study, we describe the characteristics of influenza B viruses that caused respiratory illness in the population in Italy over 13 consecutive seasons of virological surveillance, and the match between the predominant influenza B lineage and the vaccine B lineage, in each season. Trivalent seasonal influenza vaccines contain two circulating influenza A strains but a single B strain and thus provide limited immunity against circulating B strains of the lineage not included in the vaccine. Since 1985, two antigenically distinct lineages of influenza B viruses (Victoria-like and Yamagata-like) have circulated globally.

Victoria 2 how to form italy