Vaccination or mass drug administration against schistosomiasis: a hypothetical cost-effectiveness modelling comparison


Abstract

Background: Schistosomiasis is a neglected tropical disease, targeted by the World Health Organization for reduction in morbidity by 2020. It is caused by parasitic flukes that spread through contamination of local water sources. Traditional control focuses on mass drug administration, which kills the majority of adult worms, targeted at school-aged children. However, these drugs do not confer long-term protection and there are concerns over the emergence of drug resistance. The development of a vaccine against schistosomiasis opens the potential for control methods that could generate long-lasting population-level immunity if they are cost-effective.

Methods: Using an individual-based transmission model, matched to epidemiological data, we compared the cost-effectiveness of a range of vaccination programmes against mass drug administration, across three transmission settings. Health benefit was measured by calculating the heavy-intensity infection years averted by each intervention, while vaccine costs were assessed against robust estimates for the costs of mass drug administration obtained from data. We also calculated a critical vaccination cost, a cost beyond which vaccination might not be economically favorable, by benchmarking the cost-effectiveness of potential vaccines against the cost-effectiveness of mass drug administration, and examined the effect of different vaccine protection durations.

Results: We found that sufficiently low-priced vaccines can be more cost-effective than traditional drugs in high prevalence settings, and can lead to a greater reduction in morbidity over shorter time-scales. MDA or vaccination programmes that target the whole community generate the most health benefits, but are generally less cost-effective than those targeting children, due to lower prevalence of schistosomiasis in adults.

Conclusions: The ultimate cost-effectiveness of vaccination will be highly dependent on multiple vaccine characteristics, such as the efficacy, cost, safety and duration of protection, as well as the subset of population targeted for vaccination. However, our results indicate that if a vaccine could be developed with reasonable characteristics and for a sufficiently low cost, then vaccination programmes can be a highly cost-effective method of controlling schistosomiasis in high-transmission areas. The population-level immunity generated by vaccination will also inevitably improve the chances of interrupting transmission of the disease, which is the long-term epidemiological goal.

Keywords: Cost-effectiveness; Modelling; Schistosomiasis; Vaccine.

Conflict of interest statement

The authors declare that they have no competing interests.

Figures

Fig.?1
Fig.?1
High-transmission setting: prevalence (left) and heavy intensity infection prevalence (right) in SAC and adults during 30 years of control. Shaded regions represent the 95% prediction interval (i.e. 95% of all stochastic simulations lie within this region). a MDA targeted at SAC with 75% coverage. b Cohort vaccination (at 1- and 10 years-old). c Cohort vaccination (at 1- and 10 years-old) and a catch-up campaign in the first year. d Mass SAC vaccination, every 5 years. In all cases the vaccine is assumed to offer 10 years protection
Fig.?2
Fig.?2
High-transmission setting: prevalence (left) and heavy intensity infection prevalence (right) in SAC and adults during 30 years of control. a MDA targeted at the whole community (75% SAC coverage, 40% adult coverage). b Vaccination every 5 years, with a vaccine that offers 10 years protection, targeted at the community (75% SAC coverage, 40% adult coverage)
Fig.?3
Fig.?3
High-transmission setting: incremental cost-effectiveness diagrams across differing vaccine protection lengths (columns) and relative vaccination costs (rows), for MDA and vaccination-based strategies (points). Radial gridlines (grey) indicate equal cost-efficacy (i.e. the same number of heavy-intensity infection years averted per dollar). The cost per vaccination represents the full course of vaccine (not per dose and including delivery)
Fig.?4
Fig.?4
High-transmission setting: critical vaccination costs (comprising delivery and vaccine costs), relative to MDA, for school and community-wide strategies. Critical vaccination cost is defined by the cost, per course of vaccine, that achieves the same cost-effectiveness as MDA targeted at the relevant section of the community
Fig.?5
Fig.?5
Moderate-transmission setting incremental cost-effectiveness diagrams across differing vaccine protection lengths (columns) and relative vaccination costs (rows), for MDA and vaccination based strategies. Radial gridlines indicate locations on the plane of equal cost-efficacy. The cost per vaccination represents the full course of vaccine (not per dose and including delivery)
Fig.?6
Fig.?6
Moderate-transmission setting: critical vaccination costs (comprising delivery and vaccine costs), relative to MDA, for school and community-wide strategies. Critical vaccination cost is defined by the cost, per course of vaccine, that achieves the same cost-effectiveness as MDA targeted at the relevant section of the community
See this image and copyright information in PMC

Similar articles