Safety, Tolerability and Efficacy of PfSPZ Vaccine in Healthy Children and Infants 5 Months - 9 Years Living in Kenya

This study will be conducted in Siaya County in Nyanza Province, western Kenya. Healthy children aged 5 months through 9 years of age living within approximately 10 km of the study clinic(s) (Siaya County Referral Hospital, or Wagai dispensary, a government health facility in Wagai division) will be eligible for participation in Part 1; healthy infants aged 5 months - 12 months inclusive will be eligible for Part 2.

Part 1: Age De-Escalation and Dose Escalation Part 1 of this trial is a randomized blinded evaluation of the safety and tolerability of PfSPZ Vaccine administered by DVI in healthy children and infants living in an area of high malaria transmission. A maximum of 156 children from 5 months to 9 years inclusive at vaccination will be enrolled and randomized to receive vaccine or normal saline (NS) placebo by DVI. Total participation time in the dose escalation trial ranges from 5-16 weeks per participant from screening visit to close out or 4 - 12 weeks from enrolment to close out.

Vaccination will begin in the 5-9 year age group at a dosage of 4.5 x10\^5 PfSPZ. A single vaccination will be administered by DVI to each of 12 participants aged 5-9 years (inclusive) of age, 8 receiving PfSPZ vaccine and 4 participants receiving NS placebo by DVI, with treatment allocation randomized and double-blind. Once the initial dose has been shown to be well tolerated and without safety concerns, the next higher dose of 9.0 x 10\^5 PfSPZ will be administered to a second group of 5-9 year olds. Once this has been shown to be well tolerated and without safety concerns, the highest dose of 1.8 x 10\^6 PfSPZ will be given to a third group of 5-9 year olds and concurrently the lowest dose (1.35 x10\^5) will be given to a same-sized group of younger children aged 13-59 months. Two weeks later, this dose will be escalated to 2.7 x10\^5 PfSPZ in a second group of children aged 13-59 months. Only once this dose is shown to be well-tolerated and without safety concerns will PfSPZ Vaccine, at the lowest dose, be given to infants aged 5 - 12 months. Within each age group, dosages will increase stepwise until they reach 1.8 x 10\^6 PfSPZ, with the initiation of each group staggered by at least 2 weeks, provided that no safety thresholds are surpassed. In each dosage level, the PfSPZ Vaccine or placebo will be provided to a limited number of participants each day (e.g. 3 participants from one age group on days 1 through 4). The PfSPZ Vaccine dose will only be increased to the next dose level when safety has been assessed in subjects of the first group. The same procedures will be followed for all doses. Children in all age groups who are enrolled to receive the 2 highest doses, i.e. 9.0 x 10\^5 or 1.8 x 10\^6 PfSPZ, or placebo, will receive a second vaccination of the same dose after 8 weeks, provided the first vaccination at this dose level did not show safety signals.

Part 2: Safety and Efficacy Part of this study will be conducted in the outpatient areas of Siaya County Referral Hospital, a large referral hospital in western Kenya and in Wagai dispensary. A maximum of 416 infants from 5 M to 12 M inclusive at vaccination will be enrolled into this safety and efficacy trial and randomized to receive PfSPZ Vaccine at a dose determined during Part 1 of the trial (dose escalation), but likely to be 4.5x10\^5, 9.0 x10\^5and 1.8 x 10\^6 administered x 3 doses ; and NS placebo administered x 3 doses, all by DVI administered at 8 week intervals.

Participants (N = 416, with 104 in each study arm) will be randomly assigned in a double blinded fashion to receive one of the following PfSPZ Vaccine regimes:

Group 1 (N=104): The highest dose that is determined to be safe and well tolerated in the Part 1 trial, administered in 3 doses by DVI at 0, 8 and 16 weeks. Likely dosage will be 1.8 x 10\^6 PfSPZ per dose.

Group 2 (N=104): The second highest dose, which is half of the highest dose, administered in 3 doses by DVI at 0, 8 and 16 weeks. Likely dosage will be 9.0 x 10\^5 PfSPZ per dose.

Group 3 (N=104): A lower dose (half of the second highest dose) administered in 3 doses by DVI at 0, 8, 16 weeks. Likely dosage will be 4.5x 10\^5 PfSPZ per dose.

Group 4 (N=104): A placebo arm, will receive NS by DVI, 3 times at 8 week intervals.

Eligibility Criteria:
Inclusion Criteria:

* Healthy children 5 months - 9 years inclusive (Part 1) and healthy infants 5-12 months inclusive (Part 2)
* HIV negative
* Able to participate for the duration of the study.
* Parents/guardians over the age of 18 years able and willing to provide informed consent/permission. The consent/permission will be in writing. For adult parents or guardians who are illiterate, an impartial witness can sign the consent/permission form on behalf of the parent and the parent/guardian will provide a thumb print.

Exclusion Criteria:

* Positive HIV test or breastfeeding infants or children of a known HIV positive mother (per Kenyan guidelines, these HIV exposed breastfeeding children should be on cotrimoxazole)
* Refusal of HIV testing
* Elevated ALT (liver function test) ≥2x ULN ( ALT \>84 U/L)
* Abnormal hematological parameters defined as: hemoglobin \< 8 g/dl, WBC \<1500 / mm3, neutrophils \<750/ mm3, platelet count \<75.000/ mm3
* Abnormal renal function test with creatinine \>0.9 mg/dL
* Known sickle cell disease and other inherited blood cell disorders like thalassemia and G6PD deficiency
* Current use of systemic immunosuppressant pharmacotherapy
* Current significant medical condition (cardiac, hepatic, renal, or hematological) or evidence of any other serious underlying medical condition identified by medical history, physical examination, or laboratory examination
* History of a splenectomy
* History of neurologic disorder (including seizures, other than uncomplicated febrile seizures)
* Known allergy to any component of the vaccine formulation, history of anaphylactic response to mosquito-bites, or known allergy to first or second line anti-malarials used to treat malaria
* Plan to participate in another investigational vaccine/drug research during or within 1 month of this study end
* Prior participation in a malaria vaccine trial
* Participation in the PfSPZ Vaccine Trial Part 1 (for Part 2 only)
* History of any other illness or condition which, in the investigator's judgment, may substantially increase the risk associated with the subject's participation in the protocol or compromise the scientific objectives
* Child/orphan in institutional care