The transmission dynamics of Norovirus in England: A genotype-specific modelling study.

BACKGROUND

Norovirus is the leading cause of acute gastroenteritis cases in England and worldwide, with diverse co-circulating genotypes. Vaccine candidates targeting multiple genotypes are advancing. However, most transmission models still focus on single-strain dynamics, limiting their ability to assess the role of co-circulating strains on population burden.

METHODS

We developed an age structured multistrain transmission model that integrates norovirus genotype diversity, waning immunity, and cross-protection within genogroups. We calibrate to case and genotyping surveillance time-series data with community-wide age structured incidence estimates and cross-sectional seroprevalence among English children to capture the transmission dynamics of the main co-circulating norovirus strains in England. Using a calibrated model, we examine the case of an emerging GII.4 variant under different scenarios of transmissibility.

RESULTS

We found that on average the current GII.4 strain has an R0 of 4.8 (CrI 4.5 - 5.01). We estimate the average number of lifetime norovirus episodes per person to be 5.2 (CrI 95 % 4.5 - 6.3) in the absence of new pandemic strains, with 66 % of children in England experiencing at least one symptomatic episode by the age of four. Our sensitivity analysis and model selection suggests that cross-protection within genogroups (between strains of the same genogroup), is very limited at conferring protection. Importantly, our modelling suggests that a potential emerging variant would cause a larger first epidemic season and return to baseline levels with an increase in relative contribution of GII.4. If such variant was more transmissible, the size of the initial peak could almost double the current average epidemic peak.

CONCLUSIONS

This approach addresses key limitations of single-strain frameworks and offers a more comprehensive understanding of norovirus dynamics, improving the capacity to assess the potential population-level effects of upcoming multivalent vaccine strategies.