Co-circulation of the two influenza B lineages during 13 consecutive influenza surveillance seasons in Italy, 2004–2017

Abstract

BackgroundSince 1985, two antigenically distinct lineages of influenza B viruses (Victoria-like and Yamagata-like) have circulated globally. 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. 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.MethodsFrom 2004 to 2017, 26,886 laboratory-confirmed influenza cases were registered in Italy, of which 18.7% were type B. 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.ResultsCo-circulation of both B lineages was observed each season, although in different proportions every year. Overall, viruses of B/Victoria and B/Yamagata lineages caused 53.3 and 46.7% of influenza B infections, respectively. A higher proportion of infections with both lineages was detected in children, and there was a declining frequency of B/Victoria detections with age. A mismatch between the vaccine and the predominant influenza B lineage occurred in eight out of thirteen influenza seasons under study. Considering the seasons when B accounted for > 20% of all laboratory-confirmed influenza cases, a mismatch was observed in four out of six seasons. 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.ConclusionsThis study contributes to the understanding of the circulation of influenza B viruses in Italy. We found a continuous co-circulation of both B lineages in the period 2004–2017, and determined that children were particularly vulnerable to Victoria-lineage influenza B virus infections. An influenza B lineage mismatch with the trivalent vaccine occurred in about two-thirds of cases.

Lineage-specific protection and immune imprinting shape the age distributions of influenza B cases

“…While the incidence of medically attended infections is highest in children for both lineages, B/Yamagata appears less common than B/Victoria in teenagers and young adults but the pattern reverses in older age groups. This pattern has been observed in surveillance from the 2000s and 2010s in Oceania (Vijaykrishna et al, 2015), East Asia (Tan et al, 2013), Europe (Sočan et al, 2014; Puzelli et al, 2019) and North America (Skowronski et al, 2017). It has also been observed in isolates from sequence databases (Virk et al, 2020).…”

“…While the incidence of medically attended infections is highest in children for both lineages, B/Yamagata appears less common than B/Victoria in teenagers or young adults but more common in older age groups. This pattern has been observed in the 2000s and 2010s in Oceania (Vijaykrishna et al, 2015), East Asia (Tan et al, 2013), Europe (Socan et al, 2014; Puzelli et al, 2019) and North America (Skowronski et al, 2017) and globally in sequence databases (Virk et al, 2020). Changes in the expression of sialic acid receptors with age have been proposed to explain the lower mean age of B/Victoria cases (Vijaykrishna et al, 2015), but this explanation does not account for the higher frequency of B/Yamagata cases in middle-aged people.…”

Characterizing the transmission patterns of seasonal influenza in Italy: lessons from the last decade

“…Virological data from Italian region of Lombardy for the seasons from 2010-2011 to 2016-2017 season [13] and from the National Influenza Surveillance Scheme from 2017-2018 to 2019-2020 season [14] are used in our analysis. A comparison between national virological surveillance and virological data for Italian region of Lombardy from 2010-2011 to 2016-2017 season is reported in the Appendix [see Additional File 1: pp 4].…”

Viruses of Respiratory Tract: an Observational Retrospective Study on Hospitalized Patients in Rome, Italy

“…The identified viral agents included all the respiratory viruses commonly circulating in the community as well as in the hospital setting, namely FLU A and B viruses, RHV/EV, HCOV, RSV, HMPV, PIV and ADV, as already reported by other authors [8][9][10]. It is well known that the knowledge and monitoring of the prevalence of respiratory viruses in hospital settings is very important, as the impact of these infections in hospitalized patients can have more serious consequences than in the general population [1][2][3][4][8][9][10][11][12][13][14][15][16][17].…”