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

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BMC Infect Dis. 2019 Nov 21;19(1):990. doi: 10.1186/s12879-019-4621-z. Co-circulation of the two influenza B lineages during 13 consecutive influenza surveillance seasons in Italy, 2004-2017.

Puzelli S¹, Di Martino A², Facchini M², Fabiani C², Calzoletti L², Di Mario G², Palmieri A², Affanni P³, Camilloni B⁴, Chironna M⁵, D'Agaro P⁶, Giannecchini S⁷, Pariani E⁸, Serra C⁹, Rizzo C², Bella A², Donatelli I², Castrucci MR²; Italian Influenza Laboratory Network.
Collaborators (17)

Author information

1 Department of Infectious Diseases, Istituto Superiore di Sanit? (ISS), Viale Regina Elena 299, Rome, Italy. simona.puzelli@iss.it. 2 Department of Infectious Diseases, Istituto Superiore di Sanit? (ISS), Viale Regina Elena 299, Rome, Italy. 3 University of Parma, Parma, Italy. 4 University of Perugia, Perugia, Italy. 5 Department of Biomedical Science and Human Oncology, University of Bari, Bari, Italy. 6 University of Trieste, Trieste, Italy. 7 University of Florence, Florence, Italy. 8 Department of Biomedical Sciences for Health, University of Milan, Milan, Italy. 9 University of Sassari, Sassari, Italy.

Abstract

BACKGROUND:

Since 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.
METHODS:

From 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.
RESULTS:

Co-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.
CONCLUSIONS:

This 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.


KEYWORDS:

Influenza B virus; Influenza virological surveillance; Italy; Vaccine match; Victoria lineage; Yamagata lineage

PMID: 31752738 DOI: 10.1186/s12879-019-4621-z
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