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## Figure 2.
Sample size estimates for superiority, non-inferiority and equivalence trials of second-generation
malaria vaccines, according to different incidence risk of malaria in the first-generation
vaccine group. The figures show the estimated sample size required to detect a range of differences
in the efficacy (margin %) between a second and first-generation malaria vaccine.
The margin represents the absolute difference in the efficacy between the two vaccines
for active-controlled trials; the relative difference for each value of absolute risk
difference will therefore be greater for areas with a lower transmission (for example,
absolute risk difference of 10% units equates to a relative risk of 0.67 and 0.80
when the baseline risk is 30% and 50%, respectively). The different incidence risks
of malaria (proportion of individuals with malaria outcome during follow-up) in the
first-generation vaccine groups corresponds to the approximate baseline risk observed
in RTS,S phase II and III trials (that is, 30% and 50%) [4,5]. Sample sizes are calculated with 90% power at the 5% significance level by the authors
using STATA (StataCorp; College Station, TX, USA). Note, as the incidence risk approaches
0.5, the standard error gets marginally larger; this explains why the sample size
for the same absolute risk difference is bigger for a baseline risk of 50% compared
with 30% (for example, total sample size required for a superiority trial with risk
difference of 10% units is 778 and 1,030 for a baseline risk of 30% and 50%, respectively).
Fowkes |