The main goal of this study is to assess the efficacy of RTS,S/AS01E, a candidate vaccine against malaria caused by Plasmodium falciparum (P. falciparum), in adults positive for P. falciparum at the start of the study, but treated with anti-malarial medications to clear the parasite before receiving multiple doses of the vaccine. The goal is to overcome the reduced vaccine efficacy (hypo-responsiveness to the vaccine) reported in actively or chronically infected adults.
PATH and GlaxoSmithKline (GSK) are committed to developing a malaria vaccine to help reduce the burden of malaria disease in children and contribute to malaria elimination. GSK has developed a candidate vaccine against malaria caused by P. falciparum called RTS,S/AS01E. The vaccine has been shown to be safe in multiple trials and efficacy data in pediatric populations has led to a pilot implementation program in three African countries including Kenya. The RTS,S/AS01E vaccine mechanism of action is presumed to work on the initial sporozoite and liver stages of P. falciparum infection through neutralization of the circumsporozoite (CS) antigen on parasites invading after a mosquito bite in individuals immunized with the RTS,S/AS01E vaccine. In order to inform whether a vaccine such as RTS,S/AS01E may have a future role in malaria elimination, it will be important to establish vaccine efficacy in adults in Sub-Saharan Africa who are reservoirs of parasites and who contribute to ongoing malaria transmission. However, in previous trials, the vaccine has been less effective in adults who have had malaria before. There are probably multiple reasons for this, but one possible reason that is probably very important is that prior infection with malaria or an infection with malaria for long periods, even without symptoms of the disease, can prevent the vaccine from working properly. This study postulates that treatment of infection prior to immunization can reset the immune response leading to an improved vaccine efficacy. To evaluate this hypothesis, the study will recruit 5 groups. Groups 1 and 4 will have asymptomatic infection with P. falciparum as measured by a highly sensitive polymerase chain reaction (PCR) assay and will be treated with antimalarial medications prior to immunization with RTS,S/AS01E or the comparator rabies vaccine, respectively, with the primary objective of evaluating the vaccine efficacy of RTS,S/AS01E relative to the rabies vaccine in this context. Groups 2 and 5 will be negative for asymptomatic infection with P. falciparum as measured by a highly sensitive PCR assay and will be treated with antimalarial medications prior to immunization with RTS,S/AS01E or the comparator rabies vaccine, respectively, with the secondary objective of evaluating the vaccine efficacy of RTS,S/AS01 relative to the rabies vaccine in this context. Group 3 will have asymptomatic infection with P. falciparum as measured by a highly sensitive PCR assay but will not be treated with antimalarial medications prior to immunization with the RTS,S/AS01E vaccine; the immunological profile of this group and groups 1 and 2 will be evaluated as part of secondary and exploratory objectives. Other secondary objectives include safety assessments. The study will include an initial immunization period (vaccine given on 0, 1, and 7 month schedule with the final dose being 1/5 of the dose of the first two immunizations) followed by 6-12 months of follow-up (varying based on the number of events),
RTS,S/AS01E vaccine 0.5 mL, containing 25 μg protein comprising circumsporozoite protein (CS) and hepatitis B surface antigen (RTS,S), 25 μg monophosphoryl lipid (AMPL), 25 μg Quillaja saponaria 21 (QS21) in a liposomal formulation) for the first two immunizations. One-fifth dose RTS,S/AS01E vaccine was used for the third immunization.
Abhayrab rabies vaccine, 0.5 mL, contains 2.5 IU rabies antigen.
Dihydroartemisinin (120 mg or 160 mg based on weight) and piperaquine tetraphosphate (960 mg or 1280 mg based on weight) mg) administered once a day for 3 days. DHA/Pip is a long acting anti-malarial used to clear asexual stage and young gametocyte parasites.
Lucas O Tina
Kisumu, Kisumu County, Kenya
Time to First PCR-detectable Malaria Infection During the Active Detection of Infection (ADI) Phase in Groups 1 and 4
Participants were actively monitored for malarial infection starting 2 weeks after the third vaccination. Blood samples were assayed using a highly sensitive polymerase chain reaction (PCR) (Plasmodium falciparum/ Pan-Plasmodium 18S ribosomal ribonucleic acid (rRNA) laboratory developed test \[LDT\]) that can detect sub-clinical parasitemia at the US Army Medical Research Directorate-Africa (USAMRD-A) / Kenya Medical Research Institute (KEMRI) laboratories in Kisumu, Kenya. A positive PCR result from blood samples collected during the ADI was recorded as a positive event for the presence of P. falciparum blood stage infection. The time to first malaria infection is expressed in terms of rate of first malaria infection, that is, the number of malaria infection events reported over the time period elapsed until the event occurred (i.e. events per Persons Year at Risk \[PYAR\]) for each group.
Time frame: The active detection of infection phase began 2 weeks after the third vaccination (approximately week 30) for up to 35 weeks. Participants provided blood samples every 21 days during the ADI phase for PCR assays.
Time to First PCR-detectable Malaria Infection During the Active Detection of Infection Phase in Groups 2 and 5
Participants were actively monitored for malarial infection starting 2 weeks after the third vaccination. Blood samples were assayed using a highly sensitive PCR (Plasmodium falciparum/ Pan-Plasmodium 18S rRNA LDT) that can detect sub-clinical parasitemia. A positive PCR result from blood samples collected during the ADI phase was recorded as a positive event for the presence of P. falciparum blood stage infection. The time to first malaria infection is expressed in terms of rate of first malaria infection, that is, the number of malaria infection events reported over the time period elapsed until the event occurred (i.e. events per Persons Year at Risk \[PYAR\]) for each group.
Time frame: The active detection of infection phase began 2 weeks after the third vaccination (approximately week 30) for up to 35 weeks. Participants provided blood samples every 21 days during the ADI phase for PCR assays.
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Study Type
INTERVENTIONAL
Allocation
RANDOMIZED
Purpose
OTHER
Masking
NONE
Enrollment
620
Artemether (80 mg) and lumefantrine (480 mg) administered twice a day for 3 days. Coartem is a short-acting artemisinin combination therapy used to provide clearance of blood stage parasites in order to establish a clean baseline for determination of vaccine efficacy.
One dose of 15 mg primaquine. Low dose primaquine (LD PQ) is used to clear mature gametocytes of P. falciparum.
Number of Participants With Serious Adverse Events (SAEs)
An adverse event is any untoward medical occurrence in a study participant, temporally associated with the use of a medicinal product, whether or not considered related to the medicinal product, or temporally associated with a study procedure. A serious adverse event is any adverse event that: * Resulted in death, * Was life-threatening, * Resulted in disability/incapacity, * Required hospitalization or prolongation of existing hospitalization, * Resulted in disability/incapacity. * Resulted in a congenital anomaly and / or birth defect.
Time frame: From first dose to end of study, up to 65 weeks.
Number of Participants With Solicited Local and Systemic Adverse Events (AEs)
Solicited AEs are pre-specified local and systemic AEs that occur relatively more frequently or are known to be associated with immunization, which are monitored actively as potential indicators of vaccine reactogenicity. Solicited local and general AEs were collected among RTS,S vaccinated groups in the first 50 participants enrolled in Groups 1 and 2 and all participants enrolled in Group 3 (Reactogenicity Cohort) for seven days (day of vaccination and six subsequent days) after each dose of vaccine. Local (injection site) adverse events are defined as: * Pain at injection site * Swelling at injection site Systemic adverse events are defined as: * Fever (temperature ≥ 37.5°C) * Headache * Gastrointestinal problems * Fatigue * Muscle ache
Time frame: Within 7 days after each vaccination.
Number of Participants With Unsolicited Adverse Events
An adverse event is defined as any untoward medical occurrence in a study participant, temporally associated with the use of a medicinal product, whether or not considered related to the medicinal product, or temporally associated with a study procedure. Unsolicited AEs are any AEs reported spontaneously by the participant, observed by the study staff during study visits or those identified during review of medical records or source documents. Solicited AEs with an onset after the seven-day solicitation period were also considered unsolicited AEs.
Time frame: Within 28 days after each vaccination.
Geometric Mean Titer of Anti-Plasmodium Falciparum Circumsporozoite (CS) Antibodies in Groups 1, 2, and 3
The RTS,S antigen consists of sequences of both the P. falciparum circumsporozoite protein and hepatitis B surface antigen. Antibody levels against P. falciparum circumsporozoite (CS) protein central repeat region (NANP) were measured from blood samples of participants in Groups 1, 2 and 3 using standard enzyme-linked immunosorbent assays (ELISA) at Walter Reed Army Institute of Research (WRAIR), in Silver Spring, MD, United States.
Time frame: Baseline, Day 29 (28 days after first vaccination), Day 57 (28 days after second vaccination), Day 197 (24 weeks after second vaccination), and Day 225 (28 days after third vaccination)
Anti-Plasmodium Falciparum Circumsporozoite (CS) Antibody Avidity Index in Groups 1, 2, and 3
Antibody levels against P. falciparum circumsporozoite (CS) protein central repeat region (NANP) measured by standard enzyme-linked immunosorbent assays (ELISA) for participants in Groups 1, 2 and 3. To measure antibody-antigen avidity (strength of binding) ELISA was performed with and without urea (to dissociate the antigen-antibody complex). The avidity index is calculated by dividing the serum titer obtained in the presence of the urea by the serum titer without urea.
Time frame: Baseline, Day 29 (28 days after first vaccination), Day 57 (28 days after second vaccination), Day 197 (24 weeks after second vaccination), and Day 225 (28 days after third vaccination)
Geometric Mean Titer (GMT) of Anti-Hepatitis B Surface Antigen (HBsAg) Antibodies in Groups 1, 2, and 3
The RTS,S vaccine antigen consists of sequences of both the P. falciparum circumsporozoite protein and hepatitis B surface antigen, hence anti-HBsAg antibodies were also measured. Anti-hepatitis B surface antigen antibodies were assessed at the International AIDS Vaccine Initiative Human Immunology Laboratory (IAVI-HIL) at Imperial College, London, UK, using a commercially available ELISA kit.
Time frame: Baseline, Day 29 (28 days after first vaccination) and Day 225 (28 days after third vaccination)