Course of illness in the volunteer and in vitro growth inhibition on P. falciparum exhibited by the volunteer's sera. (a) Plasmodium vivax parasitaemias (percentage of infected red blood cells) determined microscopically in the volunteer are represented by a line, while detection of P. vivax by PCR is denoted by horizontal black bars. (b) Body temperatures measured at the time of phlebotomies are shown. (c) The solid line represents the average of in vitro growth inhibition obtained from four cultures, while the dotted lines represent standard errors. The broken line denotes the upper 95% confidence limit of the baseline sera. Days of high values are denoted on the symbols in this and subsequent figures. Day 0 is the day of challenge.