The study was terminated due to administrative delays in the approval of a substantial amendment to extend the shelf-life of Pvs25-IMX313. Regulatory approval was only received on 11 August 2023, after end of study visits had already been conducted.

This is an open-label, single-centre, non-randomised, first-in-human Phase Ia study to assess the safety and immunogenicity of the Pvs25-IMX313 vaccine, administered in Matrix-M1 adjuvant.

Volunteers will be recruited into one of three groups (n=8-10 per group) at the Centre for Clinical Vaccinology and Tropical Medicine (CCVTM), Oxford over approximately 18 months. All volunteers will receive three doses of Pvs25-IMX313 in Matrix-M1, administered intramuscularly and given four weeks apart. Enrolment will be staggered with clinical and safety reviews, follow-up visits and monitoring via a diary card.

Inclusion Criteria:

• Healthy adult aged 18 to 45 years.
• Able and willing (in the Investigator's opinion) to comply with all study requirements.
• Willing to allow the Investigators to discuss the volunteer's medical history with their GP.
• Volunteers with the potential to become pregnant only: must practice continuous effective contraception for the duration of the study. Acceptable forms of contraception for volunteers of child-bearing potential are: Established use of oral, injected or implanted hormonal methods of contraception, Placement of an intrauterine device or intrauterine system, Male sterilization (if the vasectomised partner is the sole partner for the participant), True abstinence from sex with sperm-producing partners, when this is in line with the preferred and usual lifestyle of the participant (periodic abstinence and withdrawal are not acceptable methods of contraception).
• Agreement to refrain from blood donation for the duration of the study.
• Able and willing to provide written informed consent to participate in the trial.

Exclusion Criteria:

• History of clinical malaria (any species).
• Travel to a clearly malaria endemic locality during the study period or within the preceding six months.
• Use of immunoglobulins or blood products (e.g., blood transfusion) in the last three months.
• Receipt of any vaccine in the 30 days preceding enrolment, or planned receipt of any other vaccine within 30 days following each study vaccination, with the exception of --COVID-19 vaccines, which should not be received between 14 days before to 7 days after any study vaccination.
• Receipt of an investigational product in the 30 days preceding enrolment, or planned receipt during the study period.
• Concurrent involvement in another clinical trial or planned involvement during the study period.
• Prior receipt of an investigational vaccine likely to impact on interpretation of the trial data, as assessed by the Investigator.
• 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).
• History of allergic disease or reactions likely to be exacerbated by any component of the -vaccine.
• Any history of anaphylaxis in reaction to vaccinations.
• Pregnancy, lactation or intention to become pregnant during the study.
• History of cancer (except basal cell carcinoma of the skin and cervical carcinoma in situ).
• History of serious psychiatric condition that may affect participation in the study.
• Any other serious chronic illness requiring hospital specialist supervision.
• Suspected or known current alcohol abuse as defined by an alcohol intake of greater than 25 standard UK units every week.
• Suspected or known injecting drug abuse in the 5 years preceding enrolment.
• Hepatitis B surface antigen (HBsAg) detected in serum.
• Seropositive for hepatitis C virus (antibodies to HCV) at screening (unless volunteer has taken part in a prior hepatitis C vaccine study with confirmed negative HCV antibodies prior to participation in that study, and negative HCV ribonucleic acid (RNA) PCR at screening for this study).
• Volunteers unable to be closely followed for social, geographic or psychological reasons.
• Any clinically significant abnormal finding on biochemistry or haematology blood tests, urinalysis or clinical examination. In the event of abnormal test results, confirmatory repeat tests will be requested. Procedures for identifying laboratory values meeting exclusion criteria are shown in SOP VC027.
• Any other significant disease, disorder, or finding which may significantly increase the risk to the volunteer because of participation in the study, affect the ability of the volunteer to participate in the study or impair interpretation of the study data.
• Inability of the study team to contact the volunteer's GP to confirm medical history and safety to participate.

Vaccination and re-vaccination exclusion criteria:

Absolute contraindications:

• Anaphylactic reaction following administration of vaccine
• Pregnancy

Contraindications at that point in time (may be rescheduled):

• Acute disease (moderate/severe illness with or without fever)
• T>37.5C
• Current COVID-19 infection, defined as ongoing symptoms with positive COVID-19 PCR swab test taken during current illness or positive COVID-19 PCR swab or rapid antigen test within preceding 7 days without symptoms. Vaccinations will be delayed by a minimum of 7 days from the date of the first positive COVID-19 PCR swab or rapid antigen test, as long as symptoms are improving or resolved. It will be at the discretion of the Investigator to withdraw a participant if they develop severe COVID-19 disease.

Solicited adverse event data was collected for 7 days post-vaccination. Unsolicited adverse event data was collected for 28 days post-vaccination.

Solicited adverse events, along with severity and the number of participants affected per study group by each event, have been reported as part of the primary outcome measures.