A norovirus intervariant GII.4 recombinant in Victoria, Australia, June 2016: the next epidemic variant?

Abstract

A norovirus recombinant GII.P4_NewOrleans_2009/GII.4_Sydney_2012 was first detected in Victoria, Australia, in August 2015 at low frequency, and then re-emerged in June 2016, having undergone genetic changes. Analysis of 14 years’ surveillance data from Victoria suggests a typical delay of two to seven months between first detection of a new variant and occurrence of a subsequent epidemic linked to that variant. We consider that the current recombinant strain has the potential to become a pandemic variant.

Genetic and Epidemiologic Trends of Norovirus Outbreaks in the United States from 2013 to 2016 Demonstrated Emergence of Novel GII.4 Recombinant Viruses

“…Not surprisingly, there was more sequence variability among GII.4 viruses harboring the GII.Pe and GII.P4 New Orleans polymerases in this study which have been circulating much longer than viruses with the GII.P16 polymerase. Taken together, the three GII.4 Sydney viruses identified in our study appear to be antigenically similar, in contrast with findings reported elsewhere (39). If these in silico findings are bona fide and if polymerase switching occurs without significant antigenic variation, vaccine development efforts may become more complicated.…”

GII.4 norovirus recombinant causes gastroenteritis epidemic in Eastern Australia, winter 2017

“…A comparison of the 2017 strains of the GII.P4_NewOrleans_2009/GII.4_Sydney_2012 recombinant with the previously reported “Melb2016” strain (Figure ) indicated that there were two subsequent variants of the recombinant. The original recombinant “Melb2016” strain and an early 2017 strain of the recombinant (the “intermediate” strain) were transient, with the emergence of a further altered strain first appearing in March 2017 (the “epidemic” strain). This epidemic strain was associated with the majority of norovirus positive outbreaks from May onwards.…”

“…Seasonality data (Figure ) showed that 2017 has had a distinctive peak in norovirus outbreaks, with a sharp rise occurring in May followed by 2 months of high norovirus activity, and a decline beginning in August. Sequence analysis of strains in this study has demonstrated that this peak was primarily due to the recombinant GII.P4_NewOrleans_2009/GII.4_Sydney_2012, the epidemic potential of which was first identified in 2016; however, this “Melb2016” strain has since undergone changes.…”

“…The study also noted that a newly detected GII.4 recombinant form (GII.P4_NewOrleans_2009/GII.4_Sydney_2012) was first detected in Victoria, Australia, in August 2015 at low frequency and then re‐emerged in June 2016, having undergone genetic change in the capsid region. The authors of the study proposed that this recombinant had the potential to become a new epidemic variant form . In the current study of norovirus outbreaks in Victoria, Australia, we investigate the contribution of this recombinant strain to outbreaks in 2017.…”

“…While intermediate or early forms of a new variant may circulate up to 18 years prior to their emergence as an epidemic strain, once present in its epidemic form, a recent study determined that a variant will typically show a delay of 2‐7 months between the first detection of a new GII.4 epidemic variant and the subsequent norovirus epidemic linked to that variant. The study also noted that a newly detected GII.4 recombinant form (GII.P4_NewOrleans_2009/GII.4_Sydney_2012) was first detected in Victoria, Australia, in August 2015 at low frequency and then re‐emerged in June 2016, having undergone genetic change in the capsid region. The authors of the study proposed that this recombinant had the potential to become a new epidemic variant form .…”