The data presented here includes all AEs, even if a volunteer subsequently dropped out of the study. Where an AE stopped and restarted within 30 days of vaccination it has only been reported once in these results, but durations have been summed. AE durations have been rounded up to the nearest day. Volunteers underwent

P. falciparum sporozoite challenge at Imperial College, London two weeks after the final vaccination. They each received bites from five mosquitoes subsequently confirmed to have more than 100 sporozoites per paired salivary gland. Anopheles stephensi mosquitoes were infected with the chloroquine-sensitive 3D7 strain Venetoclax clinical trial of the parasite at the Walter Reed Army Institute of Research (WRAIR), Maryland, US and reared in the laboratory as previously described [18]. Volunteers began attending clinic for malaria screening from the evening of day 6 after infection. At each visit they were questioned about possible symptoms, had their temperature, pulse and blood pressure measured and gave blood find more for both thick film microscopy and PCR for malaria parasites. This process was repeated twice daily from day 7 to day 14 and then once daily from days 15 to 21, or until diagnosis. Two experienced

microscopists examined a minimum of 200 high power fields (100× objective) for parasite ring forms on each sample. A diagnosis of malaria was made as soon as one or more viable parasites were seen on a volunteer’s slide. Oral anti-malarial treatment was commenced on diagnosis as an outpatient with oral Riamet® (Novartis, 20 mg artemether with 120 mg lumefantrine) given at diagnosis and then approximately 8, 24, 36 and 48 h later. Artemether combination therapy was chosen in line with World Health Organisation recommendations on the treatment of uncomplicated

malaria. Volunteers returned for repeat blood film examinations daily after treatment commenced until two consecutive negative films had been seen. Quantitative real-time all PCR was performed at challenge baseline and at all post-challenge visits until treatment commenced using a method described previously [19]. Clinicians, volunteers and staff performing other assays were blinded to the PCR results during the study. Data was adjusted using a standard curve derived from counted cultured parasites in whole blood to give the number of parasites per mL of blood. The PCR data was also used to estimate overall growth rates of blood stage parasites during the challenge for each volunteer and to back-calculate a starting number of merozoites emerging into the blood (around day 6–7) and hence an estimate of the number of infected hepatocytes responsible for initial seeding of blood-stage parasite forms. The methods employed are based on an iterative adjustment model to derive a best fit curve to the measured data, as described [20]. Ex vivo IFNγ-ELISPOTs were carried out broadly as described [21].