Identifying Optimal Vaccination Strategies for Serogroup A Neisseria meningitidis Conjugate Vaccine in the African Meningitis Belt

Abstract

ObjectiveThe optimal long-term vaccination strategies to provide population-level protection against serogroup A Neisseria meningitidis (MenA) are unknown. We developed an age-structured mathematical model of MenA transmission, colonization, and disease in the African meningitis belt, and used this model to explore the impact of various vaccination strategies.MethodsThe model stratifies the simulated population into groups based on age, infection status, and MenA antibody levels. We defined the model parameters (such as birth and death rates, age-specific incidence rates, and age-specific duration of protection) using published data and maximum likelihood estimation. We assessed the validity of the model by comparing simulated incidence of invasive MenA and prevalence of MenA carriage to observed incidence and carriage data.ResultsThe model fit well to observed age- and season-specific prevalence of carriage (mean pseudo-R2 0.84) and incidence of invasive disease (mean R2 0.89). The model is able to reproduce the observed dynamics of MenA epidemics in the African meningitis belt, including seasonal increases in incidence, with large epidemics occurring every eight to twelve years. Following a mass vaccination campaign of all persons 1–29 years of age, the most effective modeled vaccination strategy is to conduct mass vaccination campaigns every 5 years for children 1–5 years of age. Less frequent campaigns covering broader age groups would also be effective, although somewhat less so. Introducing conjugate MenA vaccine into the EPI vaccination schedule at 9 months of age results in higher predicted incidence than periodic mass campaigns.DiscussionWe have developed the first mathematical model of MenA in Africa to incorporate age structures and progressively waning protection over time. Our model accurately reproduces key features of MenA epidemiology in the African meningitis belt. This model can help policy makers consider vaccine program effectiveness when determining the feasibility and benefits of MenA vaccination strategies.

Cost-Effectiveness of Alternative Uses of Polyvalent Meningococcal Vaccines in Niger: An Agent-Based Transmission Modeling Study

“…One of the limitations of our study stems from the assumption that polyvalent vaccines offer the same degree of protection against all serogroups. This assumption is consistent with existing models that aggregate serogroups into "vaccine" and "non-vaccine" type [33,40,[47][48][49] and is also necessitated by the lack of data to characterize serogroup competition [40]. As polyvalent vaccines offer protection against all meningococcal serogroups, our model only describes the circulation of one 'vaccine' serogroup.…”

Serogroup A meningococcal conjugate (PsA-TT) vaccine coverage and measles vaccine coverage in Burkina Faso—Implications for introduction of PsA-TT into the Expanded Programme on Immunization

“…A mathematical model developed to identify optimal long-term PsA-TT vaccination strategies using surveillance and carriage data from Burkina Faso demonstrated that either strategy, introduction into EPI or repeat mass campaigns, would be effective in substantially reducing MenA incidence over a 40 year period following the initial mass immunization campaign. The most effective modelled strategy is mass immunization campaigns in 1–5 year olds every 5 years, with introduction of PsA-TT into the routine EPI program resulting in higher predicted MenA incidence than periodic immunization campaigns [13]. However, there is limited data on the duration of protection following PsA-TT vaccination, and thus forecasts of vaccine program impact may vary depending on assumptions made about duration of protection.…”

Serogroup A meningococcal conjugate vaccines in Africa

“…This strategy might be a better option in areas where EPI vaccination coverage is low. Tartof et al developed a mathematic model of serogroup A meningitis incidence in the meningitis belt and concluded that the most effective strategy was mass vaccination of 1-to 5-year-old children every 5 years, and that introducing the vaccine in EPI programs at 9 months of age was less effective [85]. Overall vaccination coverage in Burkina Faso after MenAfriVac mass vaccination was comparable to that attained for routine measles vaccination, but regions with suboptimal vaccination coverage for measles might also be at risk for coverage below targets if MenAfriVac is introduced in EPI [69].…”