Fig. 7

Comparison of the interval (in days) from last immunization to CHMI for individuals immunized in 1999–2002 (this study) and 1989–1999. The relationship between total number of mosquito bites and days after CHMI and protective efficacy is shown for the 1999–2002 study (a) and the 1989–1999 studies [15] (b). The threshold number that induced up to 93 % protection in previous studies [15] is indicated by a dotted vertical line. Protected subjects are shown as blue dots, and non-protected subjects are shown as red dots. For both studies, subjects were predominantly protected when CHMI was less than 28 days, and were predominantly not protected more than 28 days, after the last immunization, shown by the horizontal dotted line. However, these differences were not statistically significantly different in either study using the Mann–Whitney U test. c Protected and non-protected subjects in the 1999–2002 and 1989–1999 studies are combined, and grouped according to time of CHMI in days after the final immunization; the median time in days is shown for each group as colour-coded horizontal lines, and the difference was significant (P = 0.001) using Mann–Whitney U test