van Beek J, et al. - In order to ascertain a detailed understanding of global genetic diversity of noroviruses and develop a vaccine for norovirus, their epidemiology and diversity using surveillance data from the NoroNet network were analyzed. Researchers identified continuous changes in the global norovirus genetic diversity highlighting the necessity for sustained global norovirus surveillance, including assessment of possible immune escape and evolution by recombination, to provide a full overview of norovirus epidemiology for future vaccine policy decisions.

Methods

• Genetic sequences of norovirus specimens obtained from outbreak investigations and sporadic gastroenteritis cases between 2005 and 2016 in Europe, Asia, Oceania, and Africa were included.
• Norovirus sequences were genotyped and sequences that overlapped at open reading frame (ORF) 1 and ORF2 were analysed.
• Furthermore, the sampling date and country of origin of the first reported sequence were ascertained to assess when and where novel drift variants originated.

Results

• Between Jan 1, 2005, to Nov 17, 2016, 16,635 norovirus sequences were submitted, of which 1,372 (8·2%) sequences belonged to genotype GI, 15,256 (91·7%) to GII, and seven (<0·1%) to GIV.1.
• They noted that 26 different norovirus capsid genotypes circulated and 22 different recombinant genomes during this period.
• Up to 2012, but not afterwards, GII.4 drift variants emerged with 2–3-year periodicity.
• Through recombination, the GII.4 Sydney capsid appears to persist; with a novel recombinant of GII.P16–GII.4 Sydney 2012 variant detected in 2014 in Germany (n=1) and the Netherlands (n=1), and again in 2016 in Japan (n=2), China (n=8), and the Netherlands (n=3).
• In Asia in 2014, the novel GII.P17–GII.17 was first reported; it has circulated widely in Europe in 2015–16 (GII.P17 made up a highly variable proportion of all sequences in each country [median 11·3%, range 4·2–53·9], as did GII.17 [median 6·3%, range 0–44·5]).
• In health-care settings, GII.4 viruses were more common in outbreaks (2239 [37·2%] of 6022 entries) compared with other genotypes (101 [12·5%] of 809 entries for GI and 263 [13·5%] of 1,941 entries for GII non-GII.Pe–GII.4 or GII.P4–GII.4).