In low-and middle-income countries, cost-effectiveness analyses of new vaccine introduction have typically compared vaccine against doing nothing. We illustrate the impact of competing new vaccines against other realistic prevention alternatives, using maternal GBS vaccination, which is currently in trials including in South Africa, as an example.
Method:
We developed a probabilistic decision-analytic model for an annual cohort of pregnant women and their babies that simulates maternal GBS colonization status and the natural history of early onset (EOGBS) and late onset GBS disease (LOGBS) in infants. We compared four strategies: doing nothing; risk factor-based intrapartum antibiotic prophylaxis (RFB-IAP) which is used in some South African hospitals; the potential new maternal GBS vaccine; and vaccination plus RFB-IAP.
Result:
Compared to doing nothing, RFB-IAP would prevent 10% of EOGBS/LOGBS cases in South African infants, vaccination 42%, and vaccination plus RFB-IAP 48%. Incremental comparisons show that RFB-IAP would cost $240 per DALY averted compared with doing nothing (2010 US$); at a vaccine price of $20/dose, RFB-IAP alone has the highest probability of being cost-effective when willingness-to-pay falls between $280 and $1,800. Vaccination alone would cost $1,998/DALY compared with RFB-IAP alone. Vaccination plus RFB-IAP would cost $596/DALY compared with vaccination alone. The weak domination of vaccination alone does not, in this case, point to a realistic policy alternative; vaccination is delivered months before delivery and RFB-IAP given at delivery, based on risk factors present at that time.
Conclusion:
Vaccination would be very cost-effective in South Africa by World Health Organization’s gross domestic product-based guidelines. Interpretation of this finding is influenced by inclusion of an alternative, RFB-IAP. Although it prevents only 10% of cases, RFB-IAP is the most cost-effective alternative to doing nothing. The combined strategy of vaccination plus RFB-IAP prevents more disease and costs more than vaccination alone, and is consistently very cost-effective. Realistic comparators in addition to doing nothing should be included in cost-effectiveness analyses of vaccines whenever possible, to provide low- and middle-income countries’ decision makers with more complete information about policy alternatives.