Malaria vaccine efficacy: the difficulty of detecting and diagnosing malaria

Malaria Journal

Table 2 Errors in density measurement have little impact on vaccine efficacy calculated by attributable fraction.

Mode of action of vaccine	True VE	Lower limit	Upper limit
30% reduction in density 25% reduction in febrile episodes	39.8	39.3	40.3
50% reduction in density 50% reduction in febrile episodes	89.5	89.5	89.5
70% reduction in density 25% reduction in febrile episodes	89.4	88.9	89.8

$V E = 1 - [\frac{A F_{V} \times N_{V}}{A F_{U V} \times N_{U V}}]$ , where AF is the attributable fraction, N is the total number of febrile episodes and V and UV designate vaccinated and unvaccinated groups, respectively. The vaccine efficacy in the absence of measurement error and the upper and lower bounds that may be observed due to measurement error are reported for different levels of reduction in parasite density and number of febrile episodes. The data from Smith et al [21] are used to fit the logistic regression model of the probability of fever as a function of parasite density. Density data is simulated by randomly choosing cases from specific density categories using a very large data set of febrile patients in order to match the proportions of the above data set.

ISSN: 1475-2875