Community transmission of rotavirus infection in a vaccinated population in Malawi: a prospective household cohort study

Background Rotavirus vaccine effectiveness (VE) is reduced among children in low-income countries (LICs). Indirect (transmission-mediated) effects of rotavirus vaccine may contribute to the total population impact of vaccination. We estimated the effectiveness of rotavirus vaccine in preventing transmission of rotavirus to household contacts in Blantyre, Malawi. Methods We recruited vaccine-age-eligible children with acute rotavirus gastroenteritis (case-children), together with their household contacts. Clinical data and stool samples were collected from case-children at presentation, and prospectively from household contacts over 14 days. A single stool sample was collected from control households containing asymptomatic children age-matched to case-children. Samples were tested for rotavirus using real-time PCR. Risk factors for household transmission of rotavirus infection and clinical rotavirus disease were identified using logistic regression. Vaccine effectiveness against transmission (VE T ) was estimated as one minus the ratio of secondary attack rates (SAR) in vaccinated and unvaccinated populations, using VE estimates from the associated diarrhoeal surveillance platform to estimate the counterfactual SAR without vaccination. Findings A total of 196 case-households and 55 control-households were recruited. Household SAR for rotavirus infection was high (65%); SAR for clinical disease was much lower (5%). Asymptomatic infection in control households was common (28%). Increasing disease severity was associated with increased risk of transmission of both rotavirus infection and disease to household contacts. Estimated VE T was 39% (95% confidence interval 16-57%). Interpretation Rotavirus vaccine has the potential to substantially reduce household rotavirus transmission. This should be considered in clinical and health economic assessments of vaccine impact. Funding Wellcome Trust and NIH/NIAID.