Minimal Antigenic Evolution after a Decade of Norovirus GII.4 Sydney_2012 Circulation in Humans

Area of Science:

• Virology
• Immunology
• Epidemiology

Background:

• Norovirus, a leading cause of gastroenteritis, exhibits significant genetic diversity, hindering vaccine development.
• The GII.4 norovirus genotype, responsible for numerous outbreaks, has seen the emergence of antigenically distinct variants, including the Sydney_2012 strain, which has been prevalent for over a decade.

Purpose of the Study:

• To investigate the genetic and antigenic diversification of the GII.4 Sydney_2012 norovirus variant.
• To assess whether the Sydney_2012 variant has undergone significant antigenic changes despite its prolonged circulation.

Main Methods:

• Phylogenetic analysis of 1449 GII.4 Sydney_2012 norovirus capsid sequences.
• Identification of variable residues and mapping to known antigenic sites.
• Testing of virus-like particles (VLPs) with engineered mutations against polyclonal sera and monoclonal antibodies.

Main Results:

• Phylogenetic analysis revealed scattered Sydney_2012 strains without distinct yearly or geographical clusters.
• Four out of six major antigenic sites showed mutations, with specific residues (297 and 372) in antigenic site A changing over time.
• VLPs with Sydney_2012 mutations exhibited minimal changes in reactivity with polyclonal sera, and only four monoclonal antibodies lost binding, all associated with antigenic site A.

Conclusions:

• The GII.4 Sydney_2012 norovirus variant demonstrates minimal antigenic diversification despite over a decade of circulation.
• Mutations in key antigenic sites have not significantly altered the virus's overall antigenic profile.
• Findings provide crucial insights into norovirus diversification mechanisms, potentially guiding the development of broadly protective norovirus vaccines.