Rotavirus vaccine, RV1 (Rotarix), was included in the immunisation programs in Western Australia (WA) and New South Wales from mid-2007. In WA, RV1 was replaced with RV5 (RotaTeq) in mid-2009. Marked declines in rotavirus-related hospitalisations in both Aboriginal and non-Aboriginal children have been demonstrated following the implementation of the program.
Objectives and Approach
We aimed to assess RV1 vaccine effectiveness (VE) against rotavirus-coded hospitalisations among Aboriginal and non-Aboriginal children aged (1-hazard ratio*100) were obtained from Cox proportional hazards models (adjusted for infant, maternal and demographic factors and stratified by state of birth) for Aboriginal and non-Aboriginal children.
There were a total of 623 rotavirus-coded hospitalisations among the cohort children aged <2 years. Rotavirus hospitalisation rates were 143.0/100,000 child-years (95% confidence interval [CI]: 113.3-180.4) among Aboriginal children and 49.0/100,000 child-years (95% CI: 44.8-53.5) among non-Aboriginal children.
Compared to unvaccinated children, 1-dose VE among Aboriginal children against rotavirus-coded hospitalisations was 52.1% (95% CI: -0.02-77.1%) and 2-dose VE was 62.4% (95% CI: 26.9-80.7%) adjusting for birthweight, region of residence, socio-economic status, and year of birth. Among non-Aboriginal children, 1-dose VE was 39.0% (95% CI: 13.1-57.2%) and 2-dose VE was 53.4% (95% CI: 38.1-65.1%) adjusting for birth weight, mode of delivery and maternal age at birth and year of birth.
Burden of rotavirus gastroenteritis remains significant in Aboriginal children. Given the previously demonstrated declines in rotavirus-related hospitalisations in this population following vaccine introduction, our lower-than-expected VE estimates might represent bias introduced by differences in health-seeking behaviour between the vaccinated and unvaccinated, herd immunity and/or possible non-differential misclassification of the outcome.