Novel variants of respiratory syncytial virus A ON1 associated with increased clinical severity of bronchiolitis

Objective: to study RSV-A genotype ON1 genetic variability and clinical severity in infants hospitalized with bronchiolitis, over six epidemic seasons (2012-2013 to 2017-2018). Methods: From prospectively enrolled term infants hospitalized for bronchiolitis, samples positive to RSV-A ON1 (N=139) were sequenced in the second half of the G gene. Patients' clinical data were obtained from medical files and each infant was assigned a clinical severity score. ANOVA comparison and adjusted multinomial logistic regression were used to evaluate clinical severity score and clinical parameters. Results: The phylogenetic analysis of 54 unique strains showed three distinct clades, in which sequences of the last two seasons set apart from the others. The most divergent and numerous cluster of 2017-2018 strains was characterized by a novel pattern of amino acid (aa) changes, some of which located in antigenic sites. Several aa changes altered predicted glycosylation sites; divergent lineages were characterized by the acquisition of around ten new O-glycosylation sites. Clinical severity of bronchiolitis increased in the 2016-2017 and 2017-2018 seasons and changed according to the epidemic seasons only. Conclusion: The aa changes detected in the hypervariable part of the G protein may have altered functions and/or changed its immunogenicity determining an impact on disease severity.