Table 1.
Vaccine biological effects.
Fig 1.
Population-level impact of Base Case Vaccine (BCV) administered in the simulated Kenyan community.
The impact is shown on (A) human host prevalence, (B) patent snail prevalence, (C) the number of eggs/10-ml sample/person (mean intensity) and (D) the number of new worms acquired per person per year (incidence). The vaccine’s efficacies are SE = FE = ME = 80%, with a mean duration of protection (D) of ten years. Two schedules with universal coverage are shown: mass vaccination every 10 years for three rounds of vaccination (Mass BCV every 10 years) and vaccination of newborns (BCV in childhood). Pre-control endemic values were 71% prevalence, 1% snail patency, 152 eggs/10-ml sample/person mean intensity, and 3.3 worms/person/year incidence.
Fig 2.
The effect of coverage level attained in mass vaccination rounds on the population-level impact of Base Case Vaccine (BCV).
The impact at different coverage levels is shown on (A) human host prevalence, (B) patent snail prevalence, (C) the number of eggs/10-ml sample/person (mean intensity) and (D) the number of new worms acquired per person per year (incidence). The vaccine’s efficacies are SE = FE = ME = 80%, with a mean duration of protection (D) of ten years. Rounds of mass vaccination campaigns are assumed every 10 years at coverage levels of 20%, 60%, 80% and universal coverage. The percentage vaccinated is assumed to be randomly assigned.
Fig 3.
The effect of higher vaccination frequency using the Base Case Vaccine (BCV) on four outcomes.
The base case vaccine with a mean duration of protection of ten years (D = 10) is given according to different mass vaccination frequencies every ten, five and one years with universal coverage in each round. The panels indicate the impact of vaccination on (A) human host prevalence, (B) patent snail prevalence, (C) mean intensity of human infection (eggs/10-ml sample/person or e/s/p) and (D) incidence measured as the number of new worms acquired per person-year (w/p-y).
Fig 4.
The effect of shorter duration of vaccine effect on four outcomes.
The vaccine is assumed to have different durations of effect, either 10, 5, or 2 years, with the mass vaccination administered at frequency intervals set equal to vaccine durability (adaptive vaccination frequency) with universal coverage in each round. The panels indicate the impact of vaccination on (A) human host prevalence, (B) patent snail prevalence, (C) mean intensity of human infection (eggs/10-ml sample/person or e/s/p) and (D) incidence measured as the number of new worms acquired per person-year (w/p-y).
Fig 5.
The effect of sub-maximal coverage when vaccination is targeted to high-risk age groups.
Our predictions comparing a mass vaccination schedule with universal coverage (blue solid line, corresponding to predictions in Fig 1) versus targeted universal vaccination of persons of age 5–24 every 10 years (red dash-dotted line) or every 5 years (green dotted line). The panels indicate the impact of vaccination on (A) human host prevalence, (B) patent snail prevalence, (C) mean intensity of human infection (eggs/10-ml sample/person or e/s/p) and (D) incidence measured as the number of new worms acquired per person-year (w/p-y).
Fig 6.
Predicted impact of mass vaccination with universal coverage in diverse schistosomiasis endemic settings at years 2, 12 and 22 following one, two, or three mass vaccination rounds, respectively.
By increasing the transmission parameters, different endemic settings with different contact rates—represented by the pre-vaccination host intensity in the abscissa—were generated. The absolute drop in host prevalence (panel A), absolute drop in patent snail prevalence (panel B), and the absolute drop in mean number of eggs/10-ml sample/person (panel C) are calculated at years 2, 12 and 22 by subtracting the value post-intervention from the value pre-intervention. Panel D shows the number of vaccinations needed in the first round to prevent the accrual of one new worm by persons in the community during one year after the first round of vaccination.
Fig 7.
The impact of vaccination in terms of four outcomes in the short-term (year 2) and the long-term (year 22) at different assumptions of vaccine efficacies.
The vaccine durability and the frequency of mass vaccination are both assumed to be 10 years assuming universal coverage in each round of vaccination. The unit (e/s/p) stands for the number of eggs per 10ml sample per person and (w/p-y) stands for the number of new worms acquired per person-year.
Fig 8.
The impact of combined intervention (PZQ + vaccine) on four outcomes.
The panels indicate the impact of different interventions on (A) human host prevalence, (B) patent snail prevalence, (C) mean intensity of human infection (eggs/10-ml sample/person or e/s/p) and (D) incidence measured as the number of new worms acquired per person-year (w/p-y). Vaccine durability in years is indicated in the legend by the value of D. For comparison we included a scenario of base case vaccine (BCV) without MDA (a vaccine with 80% efficacy and 10-year durability offered in mass campaigns every 10 years) shown as blue dashed line without markers. Universal coverage is assumed in each round of intervention. To compare the additional impact of vaccines relative to PZQ-only interventions, a corresponding figure without vaccine intervention (PZQ-only) is provided in S3 Fig.