Figure 2: Vaccine efficacy assessments by time to microscopic patency and PCR measures.

Kaplan–Meier log-rank comparison of days to positive blood film (a) and >20 parasites per ml by PCR (b) between adenovirus-MVA prime-boost (Ad-M) group (n=14), adenovirus-only (Ad) group (n=10) and controls (n=12). Mean days to positivity by blood film: Ad-M 14.6 days (95% CI: 12.3–16.8), adenovirus-alone group (Ad) 11.3 days (95% CI: 10.2–12.5), control group 11.8 days (95% CI: 10.8–12.7); and to 20 parasites per ml by PCR: Ad-M 11.6 days (95% CI: 8.5–14.7), Ad 7.8 days (95% CI: 7.0–8.6), control group 8.1 days (95% CI: 4–8.8). (c) Group mean log-transformed PCR data (error bars represent s.e.m.). Area under curve analysis of parasite densities comparing controls to vaccinees (either including (d) or excluding (e) volunteers that were sterilely protected) at days 6.5–8 (first cycle post hepatocyte release), days 8.5–10 (second cycle) and 10.5–12 (third cycle) post challenge. Over the second and third cycles, there is a significant reduction in vaccinees’ parasite densities compared with controls; the lack of significance at cycle one probably reflects low power due to very low parasite densities. Comparison of areas under curves for all three cycles combined also shows a significant reduction in parasite densities between vaccinees and controls (P=0.003 when including sterilely protected vaccinees, P=0.01 when excluding sterilely protected vaccinees, (two-tailed t-test).