Research Highlights: R21 Malaria Vaccine Shows Promising Results with Efficacy of About 75 Percent

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Colorized electron micrograph showing malaria parasite (right, blue) attaching to a human red blood cell. The inset shows a detail of the attachment point at higher magnification.
By NIAID – Malaria Parasite Connecting to Human Red Blood Cell, CC BY 2.0, https://commons.wikimedia.org/w/index.php?curid=62117171

April 25, 2021

  • Malaria is a serious and sometimes deadly disease caused by the parasite Plasmodium falciparum.
  • Malaria is usually transmitted by infected Anopheles mosquitoes.
  • The progression in controlling the disease stalled and the need for an effective and deployable vaccine has been emphasized.
  • RTS,S/AS01 is the world’s first malaria vaccine shown to provide protection against malaria in young children.[1]
  • RTS,S/AS01 is the most effective malaria vaccine up to date and showed 55.8% efficacy over 12 months in African children.
  • Researchers conducted a double-blind study of a low-dose circumsporozoite protein-based vaccine called R21.
  • Circumsporozoite protein is a secreted protein of the sporozoite stage of the malaria parasite.[2]
  • Two different doses of adjuvant, Matrix-M™, were added to the R21 vaccine.
  • An adjuvant is a substance that increases the effectiveness of a vaccine.
  • The group composed of 5 to 17 month-old children in Nanoro, Burkina Faso.
  • Prior to the malaria season, vaccinations were administered every 4 weeks.
  • Three vaccinations were administered with a fourth dose one year later.
  • Over one year, the safety, immunogenicity, and efficacy were evaluated.
  • 450 children were randomized to receive the R21-Matrix-M™ vaccine or a control rabies vaccine.
  • R21-Matrix-M™ had a 43 favorable safety profile.
  • After 6 months, 29.5% who received R21-Matrix-M™ with low dose adjuvant developed malaria.
  • 26% who received R21-Matrix-M™ with high-dose adjuvant developed malaria.
  • 71.4% who received the control rabies vaccine developed malaria.
  • On average, 72.25% who received R21-Matrix-M™ did not develop clinical malaria.
  • Vaccine efficacy was 74% and 77% in the low and high dose adjuvant groups respectively.
  • After one year, vaccine efficacy remained at 77% in the high-dose adjuvant group.
  • After 28 days from the third vaccination, the individuals showed a high concentration of malaria-specific antibodies.
  • Malaria-specific antibodies were doubled in a higher adjuvant dose.
  • Antibodies diminished however, they were boosted to levels similar to peak concentrations after the primary series of vaccinations following the fourth dose administered one year later.

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Source:

https://papers.ssrn.com/sol3/papers.cfm?abstract_id=3830681

[1] https://www.malariavaccine.org/malaria-and-vaccines/rtss

[2] Porter, Michael; Jennifer Nicki; Christopher Pool (June 2013). “Transgenic Parasites Stably Expressing Full-Length Plasmodium falciparum Circumsporozoite Protein as a Model for Vaccine Down-Selection in Mice Using Sterile Protection as an Endpoint”. Clinical and Vaccine Immunology. 20 (6): 803–810. doi:10.1128/cvi.00066-13. PMC 3675977. PMID 23536694

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