Skip to main content


Figure 1 | Malaria Journal

Figure 1

From: Synergism from combinations of infection-blocking malaria vaccines

Figure 1

Estimated efficacy against infection as a function of the average proportion of parasites killed for pre-erythrocytic (green) and blood-stage vaccines (red). (a) The number of successfully developing sporozoites is assumed to follow a Negative Binomial distribution with mean n and shape parameter r = 0.5. With a mean of n = 30 sporozoites, a pre-erythrocytic vaccine that eliminates 85% of sporozoites will prevent 20% of infections. Combining two vaccines that eliminate 85% of sporozoites via independent mechanisms will result in a multicomponent vaccine that prevents 60% of infections. The curve is convex such that incremental increases in the proportion of sporozoites eliminated translate to greater increases in efficacy against infection. (b) Blood-stage parasites are assumed to increase in number every two-day cycle by a factor equal to the parasite multiplication rate (PMR), which varies among individuals according to a Log-Normal distribution with coefficient of variation C v = 0.5. With a mean PMR = 8, a blood-stage vaccine that eliminates 75% of parasites will prevent only 10% of infections. Combining two vaccines that eliminate 75% of parasites through independent mechanisms will result in a multi-component vaccine preventing 95% of infections. The point of inflection in the curve corresponds to the proportion of BS parasites that must be eliminated to reduce the PMR below the threshold of 1.

Back to article page