Cost-effectiveness analysis of maternal immunisation against group B Streptococcus (GBS) disease: A modelling study

Background: There is a considerable global burden of invasive group B streptococcal (GBS) disease. Vaccines are being developed for use in pregnant women to offer protection to neonates. Objective: To estimate the potential impact and cost-effectiveness of maternal immunisation against neonatal and maternal invasive GBS disease in the UK. Methods: We developed a decision-tree model encompassing GBS-related events in infants and mothers, following a birth cohort with a time horizon equivalent to average life expectancy (81 years). We parameterised the model using contemporary data from disease surveillance and outcomes in GBS survivors. Costs were taken from NHS sources and research studies. Maternal immunisation in combination with risk-based intrapartum antibiotic prophylaxis (IAP) was compared to the current standard practice of risk-based IAP alone from an NHS and Personal Social Services (health-provider) perspective. We estimated the cases averted and cost per QALY gained through vaccination. One-way sensitivity analysis, scenario analysis and probabilistic sensitivity analysis were performed. Results: An effective maternal immunisation programme could substantially reduce the burden of GBS disease. The deterministic analysis estimated the threshold cost-effective price for a GBS vaccine to be £54 per dose at £20,000/QALY (£71 per dose at £30,000/QALY). Results were most sensitive to assumptions on disease incidence, sequelae rate and vaccine efficacy. Probabilistic analysis showed 90.66% of iterations fell under the £30,000 threshold at a vaccine price of £55. Inclusion of modest prevention of stillbirths and/or, preterm births, carer health impacts, maternal GBS deaths and 1.5% discounting improved cost-effectiveness compared to the base case. Lowering vaccine strain coverage made the vaccine less cost-effective. A key limitation is that the properties of the final GBS vaccine are unknown. Conclusions: Maternal GBS immunisation is expected to be cost-effective, even at a relatively high vaccine price.