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J Clin Virol. 2017 Sep;94:1-7. doi: 10.1016/j.jcv.2017.06.007. Epub 2017 Jun 29.

Changes in genetically drifted H3N2 influenza A viruses and vaccine effectiveness in adults 65 years and older during the 2016/17 season in Denmark.

Author information

1
Department of Virus and Microbiological Special diagnostics, National Influenza Center, Statens Serum Institut, Artillerivej 5, 2300 Copenhagen S, Denmark. Electronic address: ratr@ssi.dk.
2
Department of Virus and Microbiological Special diagnostics, National Influenza Center, Statens Serum Institut, Artillerivej 5, 2300 Copenhagen S, Denmark; Department of Infectious Diseases and Centre for Global Health, Clinical Institute, University of Southern Denmark, Campusvej 55, 5230 Odense M, Denmark.
3
Department of Infectious Disease Epidemiology & Prevention, Statens Serum Institut, Artillerivej 5, 2300 Copenhagen S, Denmark.
4
Department of Clinical Microbiology, Herlev Hospital, Herlev Ringvej 75, 2730 Herlev, Denmark.
5
Department of Clinical Microbiology, Slagelse Hospital, Ingemannsvej 18, 4200 Slagelse, Denmark.
6
Department of Clinical Microbiology, Aalborg University Hospital, Hobrovej 18-22, 9100 Aalborg, Denmark.
7
Department of Clinical Microbiology, Vejle Sygehus, Beriderbakken 4, 7100 Vejle, Denmark.
8
Department of Clinical Microbiology, Odense University Hospital, Søndre Blvd. 29, 5000 Odense C, Denmark.
9
Department of Clinical Microbiology, Rigshospitalet, Blegdamsvej 9, 2100 København Ø, Denmark.

Abstract

BACKGROUND:

In Denmark, influenza A virus of the subtype H3N2 has been dominating the 2016/17 season, as in most countries of the Northern Hemisphere.

OBJECTIVES:

This study was conducted as part of the Danish seasonal influenza surveillance programme to genetically characterize circulating H3N2 viruses and determine the seasonal vaccine effectiveness (VE) overall in the Danish population and further on the virus cluster level.

STUDY DESIGN:

Influenza virus positive samples submitted for the national surveillance programme were genetically characterized by sequencing. VE estimates against influenza A and the circulating virus clusters were determined in patients above 65 years using the test-negative case-control design.

RESULTS:

The genetic characterization revealed several genetically drifted viruses, which could be divided into four main clusters by the defining amino acid substitutions: 3C.2a/N121K/S144K, 3C.2a/T131K/R142K, 3C.2a1, and 3C.2a1/N121K. Some of the drifted viruses appeared to be more prominent in vaccinated or non-vaccinated individuals, respectively. Overall the adjusted VE was 7.4% (95% confidence interval (CI): -6.0-19.2) among inpatients and 19.3% (95% CI: -5.7-38.4) among outpatients, respectively. VE for the four main virus clusters was; cluster 3C.2a1: 38.8% (95% CI: -29.8-71.1), cluster 3C.2a/N121K/S144K: 9.2% (95% CI: -63.0-49.4), cluster 3C.2a/T131K/R142K: 19.0% (95% CI: -85.3-64.6), and cluster 3C.2a1/N121K: -12.2% (95%CI: -129.7-45.2).

CONCLUSIONS:

Several genetically drifted H3N2 viruses have been circulating in Denmark in the 2016-17 influenza season. An overall low VE was estimated and VE for the four main virus cluster indicate different VEs between the circulating drifted H3N2 viruses.

KEYWORDS:

Antigenic characterization; Genetic drift; Phylogeny; Seasonal influenza; Vaccine effectiveness

PMID:
28697450
DOI:
10.1016/j.jcv.2017.06.007
[Indexed for MEDLINE]

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