Emergence of unusual rotavirus G9P[4] and G8P[8] strains during post vaccination surveillance in Argentina, 2017-2018.

INTRODUCTION

In 2015, Argentina included Rotarix™ monovalent vaccine for universal administration and it showed a sharp decline in all-cause and rotavirus-confirmed cases as well as an immediate predominance of the G2P[4] genotype. The aim of this study was to analyze the impact of rotavirus vaccination on laboratory-confirmed cases and genotype distribution in Argentina following its introduction.

MATERIAL AND METHODS

Prevalence and seasonality of laboratory-confirmed rotavirus cases data were assessed. Analyses of circulating genotypes were performed by conventional binary characterization (G and P typing). Phylogenetic study of VP7 gene was performed from emergent unusual strains.

RESULTS

During 2017-2018, 1183 rotavirus cases (13.2%) were detected, and prevalence was uniform among different age subgroups. Weekly distribution showed a raise of confirmed cases around late July and early August. In 2017 the most frequently detected genotypes were G2P[4] and G3P[8]. However, in 2018 G12P[8] genotype increased and it was detected at a high rate. Noteworthy, the detection of uncommon G9P[4] and G8P[8] strains (bearing DS-1-like genetic backbones) was observed at moderate rates.

DISCUSSION

Following four years of universal vaccination, the prevalence of rotavirus remained low in children under 5 years of age with a shift of the seasonal peak in early spring. The emergence of uncommon genotypes was due to introduction of new strains rather than to reassortment of local strains. Continuous monitoring of rotavirus burden of disease and genotype distribution provides useful evidence to evaluate existing immunization strategies and to contribute in the development of new vaccines as well.