Controlled Human Malaria Infection in Semi-Immune Kenyan Adults. (CHMI-SIKA)

Inclusion Criteria: * Healthy adults aged 18 to 45 years. * Able and willing (in the Investigator's opinion) to comply with all study requirements. * Informed consent. * Use of effective method of contraception for duration of study (women only). The investigators will ask the female volunteers to come with their family planning records to verify. Effective contraception is defined as a contraceptive method with failure rate of less than 1% per year when used consistently and correctly, in accordance with the product label. Examples of these include: combined oral contraceptives; injectable progestogen; implants of etenogestrel or levonorgestrel; intrauterine device or intrauterine system; male partner sterilisation at least 6 months prior to the female subject's entry into the study, and the relationship is monogamous; male condom combined with a vaginal spermicide (foam, gel, film, cream or suppository); and male condom combined with a female diaphragm, either with or without a vaginal spermicide (foam, gel, film, cream, or suppository). Exclusion Criteria: * Use of systemic antibiotics with known antimalarial activity within 30 days of administration of PfSPZ Challenge (e.g. trimethoprim-sulfamethoxazole, doxycycline, tetracycline, clindamycin, erythromycin, fluoroquinolones and azithromycin). * Receipt of an investigational product in the 30 days preceding enrolment, or planned receipt during the study period. * Current participation in another clinical trial or recent participation within 12 weeks of enrolment. * Prior receipt of an investigational malaria vaccine. * Any confirmed or suspected immunosuppressive or immunodeficient state, including HIV infection; asplenia; recurrent, severe infections and chronic (more than 14 days) immunosuppressant medication within the past 6 months (inhaled and topical steroids are allowed). * Use of immunoglobulins or blood products within 3 months prior to enrolment. * Any serious medical condition reported or identified during screening that increases the risk of CHMI. * Any clinically significant abnormal finding on biochemistry or haematology blood tests, urinalysis or clinical examination. * Women only; pregnancy, or an intention to become pregnant during the duration of the study. * Confirmed parasite positive by PCR a day before challenge i.e. at C-1. Exclusion Criterion on Day of Challenge: • Acute disease, defined as moderate or severe illness with or without fever (temperature \>37.5°C).