Influenza B virus infections in Western Saxony, Germany in three consecutive seasons between 2015 and 2018: Analysis of molecular and clinical features

Abstract

Background: The impact of annual influenza epidemics and prevailing strains varies worldwide and regional. The majority of vaccines used contained two influenza A strains and only one influenza B strain (trivalent vaccine).

Aim: The aim of the study was to compare laboratory confirmed influenza B cases during three consecutive years with respect to vaccination history, clinical symptoms and molecular virology.

Methods: Partial HA gene sequences were analyzed for lineage determination and complete HA sequence in cases with reported vaccination and in fatal cases. Clinical data were retrieved from patient charts.

Findings: During the 2015/16 season, 75 influenza B cases were retrieved; 11 in 2016/17, and 274 in 2017/18. The frequency of Yamagata-lineage strains increased from 7.6% to 100%. No difference was detected in the relative frequency of co-morbidities in season 2017/18. 37.7% of the adult patients and 4.5% of pediatric patients were vaccinated against influenza.

Interpretation: Phylogenetically, Yamagata strains clustered similarly in 2017/2018 when compared to the previous two influenza seasons. While the relative frequency of influenza B cases differed, the clinical symptoms remained similar.

Conclusion: World Health Organization recommendations for the use of tetravalent vaccines that contain two influenza B strains (Yamagata and Victoria) in addition to the two influenza A strains (H1N1 and H3N2) should be implemented in national vaccination guidelines.

Funding: This research was partially supported by the Association of Sponsors and Friends of Leipzig University.

Keywords: Epidemiology; Influenza; Influenza B; Molecular epidemiology; Seasonal frequency; Victoria-like strains; Yamagata-like strains.

Fig. 1

Number of patients with laboratory-confirmed diagnosis of influenza B per week (columns) for season 2015/16 (A) and 2017/18 (B). The dotted lines represent the case numbers for patients under 18 years of age and the dashed lines patients that were 18 years of age and older.

Fig. 2

Relative distribution of influenza B cases by age. Season 2017/18 is represented by grey bars and the combined seasons of 2015/16 and 2016/17 are shown in white bars.

Fig. 3

Phylogenetic trees of the hemagglutinin (HA) nucleotide sequences of (A) Victoria- and (B) Yamagata-like influenza B viruses. Trees were constructed based upon nucleic acid alignments of the complete coding sequences (1710 nucleotides) of HA gene (1755 nucleotides) by the Maximum-Likelihood method. Numbers at each node represent bootstrap values obtained with 1000 replicates (values > 75 are shown). Reference strains are given at the bottom of the trees (black). Isolates from this study are labeled with the following symbols: vaccinated with trivalent vaccine (triangle), vaccinated with tetravalent vaccine (square), randomly selected case without vaccination history (circle), fatal cases (black filled symbols). Strains of season 2015/16 are shown in purple, strains of season 2016/17 are shown in green and strains of season 2017/2018 are shown in blue. Amino acid changes with regard to the vaccine strain (red) are given in brackets. The clades of the detected lineages are shown on the right (numbers). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Fig. 3

Phylogenetic trees of the hemagglutinin (HA) nucleotide sequences of (A) Victoria- and (B) Yamagata-like influenza B viruses. Trees were constructed based upon nucleic acid alignments of the complete coding sequences (1710 nucleotides) of HA gene (1755 nucleotides) by the Maximum-Likelihood method. Numbers at each node represent bootstrap values obtained with 1000 replicates (values > 75 are shown). Reference strains are given at the bottom of the trees (black). Isolates from this study are labeled with the following symbols: vaccinated with trivalent vaccine (triangle), vaccinated with tetravalent vaccine (square), randomly selected case without vaccination history (circle), fatal cases (black filled symbols). Strains of season 2015/16 are shown in purple, strains of season 2016/17 are shown in green and strains of season 2017/2018 are shown in blue. Amino acid changes with regard to the vaccine strain (red) are given in brackets. The clades of the detected lineages are shown on the right (numbers). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)