Rotavirus is the major cause of gastroenteritis in young children worldwide. The rotavirus vaccines Rotarix (monovalent G1P[8]) and RotaTeq (pentavalent) have resulted in substantial decreases in rotavirus disease. However, despite Rotarix introduction in August 2006 outbreaks of disease still occur in Central Australia.
An outbreak of rotavirus gastroenteritis occurred in Alice Springs in mid-2010 that resulted in the hospitalisation of 43 children. Vaccination records revealed 47.6% of eligible patients were vaccinated. Rotavirus genotyping identified a G1P[8] strain, whole genome sequencing of the 11 gene segments and phylogenetic analysis of representative samples revealed the genome was genetically similar to contemporary globally circulating rotavirus strains.
The correlates of rotavirus protection are not well understood; however the outer capsid proteins VP7 and VP4 are involved in protective immunity and elicit neutralizing antibodies. Sequence analysis of VP7 and VP4 of the outbreak strain compared to genes from Rotarix identified amino acid differences in antigenic regions including sites with recognised roles in neutralisation escape. Fluorescent focus neutralization was used to characterise antigenic differences between a culture adapted outbreak strain and Rotarix. A panel of VP7 N-MAbs and polyclonal sera derived to RV4 (G1P[8]) and N-MAb derived to VP4 of F45 (G9P[8]) were used. A distinct neutralization pattern was identified in the 2010 outbreak virus when compared to Rotarix, correlating with the identified amino acid changes. These data demonstrate antigenic differences in VP7 and VP4 proteins between the outbreak strain and Rotarix.
The antigenic differences in the VP7 and VP4 genes in the outbreak strain may have resulted in evasion of vaccine induced protection and facilitated the emergence of this strain. The outbreak was associated with moderate vaccine coverage and possibly low vaccine take in the population, factors that possibly contributed to the outbreak occurring.