Study of Malaria Vaccine RTS,S/AS01E in Plasmodium Falciparum-infected and Uninfected Adults Pre-treated With Anti-malarial Therapy

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),

Eligibility Criteria:
Inclusion Criteria:

* Provision of signed or thumb printed and dated informed consent form
* Stated willingness to comply with all study procedures and availability for the duration of the study
* Male or female between 18 and 55 years of age, inclusive
* In good general health as evidenced by medical history and clinical examination before entering the study
* Ability to take oral medication and be willing to adhere to the medication regimen
* For females, she must be of non-childbearing potential or use appropriate measures to prevent pregnancy for 30 days prior to vaccination through 2 months after completion of the vaccine series. Non-childbearing potential means she is surgically sterilized or at least one year post-menopausal. Appropriate measures to prevent pregnancy include abstinence or adequate contraceptive precautions (i.e. intrauterine contraceptive device; oral contraceptives; diaphragm or condom in combination with contraceptive jelly, cream or foam; Norplant or Depo-Provera). Clinical trial site staff will assist with provision of acceptable birth control for study entry and will discuss with volunteer at screening visit.

Exclusion Criteria:

* Planned administration/administration of a vaccine not foreseen by the study protocol from within 30 days before the first dose of study vaccine until 30 days after the last dose of study vaccine.†

  † In the context of the COVID-19 pandemic, the administration of the COVID-19 vaccine will be allowed as an exception to this exclusion criteria as follows. The study team will work with the participant to attempt to have any COVID-19 vaccine administration occur 30 days or more before or after study vaccinations. When this is not possible, COVID-19 vaccination will be allowed 10 days or more before or after study vaccination. Intervals shorter than 10 days can be allowed on a case-by-case basis in discussion with the sponsor.
* Any prior receipt of any rabies vaccine or experimental malaria vaccine.
* Confirmed or suspected significant immunosuppressive or immunodeficient condition as determined by the investigator, including clinical stage 3 or 4 human immunodeficiency virus (HIV) infection.
* A family history of congenital or hereditary immunodeficiency.
* History of allergic reactions, significant immunoglobulin E (IgE)-mediated events or anaphylaxis to previous immunizations.
* History of any neurologic disorders.
* Acute disease (defined as the presence of a moderate or severe illness with or without fever), including acute malaria, at the time of enrolment. All vaccines can be administered to persons with a minor illness, such as diarrhea or mild upper respiratory infection without fever, i.e. Oral temperature \< 37.5°C\*. Individuals excluded with acute disease, including acute malaria, can become eligible again after complete recovery of the illness, including appropriate treatment as applicable, and can be rescreened at a later date. \*Temperature readings may be taken by site staff either using either oral, axillary, or infrared thermal thermometers during clinic or field visits, while subjects enrolled in the reactogenicity cohort will be supplied with oral thermometers for the purposes of recording their own temperature measurements in the memory aid over 7 days after each vaccination.
* Acute or chronic, clinically significant pulmonary, cardiovascular (including cardiac arrythmias) , hepatic or renal functional abnormality, as determined by medical history, physical examination or laboratory screening tests.
* History of homozygous sickle cell disease (Hgb SS).
* Any clinically significant laboratory abnormalities as determined by the investigator on screening labs.
* History of splenectomy.
* Administration of immunoglobulins, blood transfusions or other blood products within the three months preceding the first dose of study vaccine or planned administration during the study period.
* Pregnant (i.e. a positive pregnancy test) or lactating female during immunization phase of the study (refer to section 2.3 for rationale). If a woman becomes pregnant after all vaccinations are complete, she will not be excluded from the remainder of the study.
* Female planning to become pregnant or planning to discontinue contraceptive precautions during the vaccination phase.
* History of chronic alcohol consumption and/or drug abuse.
* Chronic administration (defined as more than 14 days) of immunosuppressants or other immune-modifying drugs within six months prior to the first vaccine dose (for corticosteroids, this will mean prednisone, or equivalent, ≥ 0.5 mg/kg/day. Inhaled and topical steroids are allowed).
* Major congenital defects or serious chronic illness.
* Simultaneous participation in any other clinical trial \[apart from participation in the Health and Demographics Surveillance System (HDSS) network\].
* Any other findings that the investigator feels would increase the risk of having an adverse outcome from participation in the trial.