Table 2 Results of simulated vaccine trials
From: Measures of clinical malaria in field trials of interventions against Plasmodium falciparum
| Â | Vaccine effect | ||
|---|---|---|---|
| Â | A: Reduction in force of infection by 50% | B: Reduction in parasite densities by 50% | C: Multiplication of pyrogenic threshold by 2 |
Figure 1a: Distribution of parasite densities in the community (from which simulated datasets are sampled) | Frequency is halved at each density above zero. Frequency of zero parasite density increases to compensate. | Frequency of low parasite densities increases; frequency of high parasite densities decreases. Frequency of zero parasite density unchanged. | Same as placebo |
Figure 1b: Distribution of parasite densities in all disease cases 1b) (from which simulated datasets are sampled) | Frequency relative to that in placebo decreases with increasing parasite density. | Frequency relative to that in placebo decreases with increasing parasite density | Frequency relative to that in placebo decreases with increasing parasite density |
Figure 1c: Relative risk of given parasite density in disease cases relative to controls | At any given density, reduced relative to placebo | Same as placebo | At any given density, reduced relative to placebo |
Figure 1d: Attributable fraction of cases by parasite density (Figure 1d) | At any given density, reduced relative to placebo | Same as placebo | At any given density, reduced relative to placebo |
Figure 1e: Distribution of parasite densities in clinical malaria cases | Frequency of high parasite densities lower than in placebo | Frequency of high parasite densities lower than in placebo | Frequency of high parasite densities lower than in placebo |
Figure 1f: Sensitivity of case definition, by parasite density | Same as placebo | At any given density, reduced relative to placebo | At any given density, reduced relative to placebo |
Figure 1g: Specificity of case definition by parasite density | Same as placebo | At any given density, increased relative to placebo | Same as placebo |
Figure 1h: Efficacy estimate by parasite density cut-off (x) | Estimated efficacy increases with cut-off approximates the true efficacy at high cut-off values | Estimated efficacy increase with cut-off and exceeds the true efficacy at high cut-off values | Estimated efficacy increase with cut-off and approximates the true efficacy at high cut-off values |
Figure 1i: Power of study, by parasite density cut-off | Reaches a maximum of about 67% at a cut-off of about 10,000/μl | Reaches a maximum of about 87% at a cut-off of about 40,000/μl | Increases to 100% at a parasite density of about 60,000/μl |
Estimated efficacy using latent class model | 46.1% (18.7%) | 55.6% (23.1%) | 55.2% (16.5%) |
Power using latent class model (1-β) | 59.2% | 82.4% | 71.2% |