Date Published: January 24, 2018
Publisher: Public Library of Science
Author(s): Reza Yaesoubi, Caroline Trotter, Caroline Colijn, Maziar Yaesoubi, Anaïs Colombini, Stephen Resch, Paul A. Kristiansen, F. Marc LaForce, Ted Cohen, Lorenz von Seidlein
Abstract: BackgroundThe introduction of a conjugate vaccine for serogroup A Neisseria meningitidis has dramatically reduced disease in the African meningitis belt. In this context, important questions remain about the performance of different vaccine policies that target remaining serogroups. Here, we estimate the health impact and cost associated with several alternative vaccination policies in Burkina Faso.Methods and findingsWe developed and calibrated a mathematical model of meningococcal transmission to project the disability-adjusted life years (DALYs) averted and costs associated with the current Base policy (serogroup A conjugate vaccination at 9 months, as part of the Expanded Program on Immunization [EPI], plus district-specific reactive vaccination campaigns using polyvalent meningococcal polysaccharide [PMP] vaccine in response to outbreaks) and three alternative policies: (1) Base Prime: novel polyvalent meningococcal conjugate (PMC) vaccine replaces the serogroup A conjugate in EPI and is also used in reactive campaigns; (2) Prevention 1: PMC used in EPI and in a nationwide catch-up campaign for 1–18-year-olds; and (3) Prevention 2: Prevention 1, except the nationwide campaign includes individuals up to 29 years old.Over a 30-year simulation period, Prevention 2 would avert 78% of the meningococcal cases (95% prediction interval: 63%–90%) expected under the Base policy if serogroup A is not replaced by remaining serogroups after elimination, and would avert 87% (77%–93%) of meningococcal cases if complete strain replacement occurs. Compared to the Base policy and at the PMC vaccine price of US$4 per dose, strategies that use PMC vaccine (i.e., Base Prime and Preventions 1 and 2) are expected to be cost saving if strain replacement occurs, and would cost US$51 (−US$236, US$490), US$188 (−US$97, US$626), and US$246 (−US$53, US$703) per DALY averted, respectively, if strain replacement does not occur.An important potential limitation of our study is the simplifying assumption that all circulating meningococcal serogroups can be aggregated into a single group; while this assumption is critical for model tractability, it would compromise the insights derived from our model if the effectiveness of the vaccine differs markedly between serogroups or if there are complex between-serogroup interactions that influence the frequency and magnitude of future meningitis epidemics.ConclusionsOur results suggest that a vaccination strategy that includes a catch-up nationwide immunization campaign in young adults with a PMC vaccine and the addition of this new vaccine into EPI is cost-effective and would avert a substantial portion of meningococcal cases expected under the current World Health Organization–recommended strategy of reactive vaccination. This analysis is limited to Burkina Faso and assumes that polyvalent vaccines offer equal protection against all meningococcal serogroups; further studies are needed to evaluate the robustness of this assumption and applicability for other countries in the meningitis belt.
Partial Text: N. meningitidis remains a major cause of morbidity and mortality in the meningitis belt, a region in sub-Saharan Africa extending from Senegal to Ethiopia, with an estimated population of 400 million people . In this region, meningitis epidemics occur sporadically, resulting in tens of thousands of cases and imposing substantial economic costs to affected communities. Since the late 1970s, control of meningitis epidemics in the meningitis belt has relied on reactive vaccination campaigns using polysaccharide vaccines. These reactive campaigns are triggered once an outbreak surpasses an epidemic threshold defined by the World Health Organization (WHO). While timely implementation of this reactive strategy may blunt the severity of meningococcal epidemics [2–4], in many settings the impact of reactive vaccination campaigns is limited by delays in the diagnosis and reporting of meningitis cases and subsequent delays in the launch of these vaccination activities .
Over a 30-year simulation period in Burkina Faso using the Base strategy of the EPI with MenAfriVac and reactive immunization with PMP vaccines, we project an annual average of 5,412 meningococcal cases (95% prediction interval: 105–16,550) with strain replacement and 1,642 (32–5,794) meningococcal cases without strain replacement. Compared to a counterfactual scenario in which reactive vaccination is not used, this represents an expected reduction of 45% (26%–62%) and 43% (22%–59%) in meningococcal incidence. The relatively modest impact of this strategy is attributable to (1) delays in the launch of reactive campaigns within districts upon crossing the epidemic threshold and (2) the short duration of immunity and lack of effect on carriage offered by PMP vaccines.
While the currently recommended strategy for meningitis control in sub-Saharan Africa relies on reactive vaccination campaigns using PMP vaccines in districts where the epidemic threshold is passed, our model suggests that this approach will be outperformed by alternative policies using affordable PMC vaccines. The use of PMC vaccines in the EPI and in reactive vaccination programs could markedly reduce the public health burden of meningococcal epidemics but still leaves districts at substantial risk of sporadic outbreaks. The addition of nationwide catch-up vaccination campaigns to immunize 1–18-year-olds with PMC vaccines could prevent the majority of meningococcal cases. Our results suggest that this strategy is likely to be cost-effective (and potentially cost saving) with respect to the current WHO-recommended meningitis control strategy in sub-Saharan Africa once affordable PMC vaccine becomes available.