Immunogenicity and Protective Efficacy of Radiation-Attenuated and Chemo-Attenuated PfSPZ Vaccines in Equatoguinean Adults

Am J Trop Med Hyg. 2021 Jan;104(1):283-293. doi: 10.4269/ajtmh.20-0435.

Abstract

Plasmodium falciparum sporozoite (PfSPZ) Vaccine (radiation-attenuated, aseptic, purified, cryopreserved PfSPZ) and PfSPZ-CVac (infectious, aseptic, purified, cryopreserved PfSPZ administered to subjects taking weekly chloroquine chemoprophylaxis) have shown vaccine efficacies (VEs) of 100% against homologous controlled human malaria infection (CHMI) in nonimmune adults. Plasmodium falciparum sporozoite-CVac has never been assessed against CHMI in African vaccinees. We assessed the safety, immunogenicity, and VE against homologous CHMI of three doses of 2.7 × 106 PfSPZ of PfSPZ Vaccine at 8-week intervals and three doses of 1.0 × 105 PfSPZ of PfSPZ-CVac at 4-week intervals with each arm randomized, double-blind, placebo-controlled, and conducted in parallel. There were no differences in solicited adverse events between vaccinees and normal saline controls, or between PfSPZ Vaccine and PfSPZ-CVac recipients during the 6 days after administration of investigational product. However, from days 7-13, PfSPZ-CVac recipients had significantly more AEs, probably because of Pf parasitemia. Antibody responses were 2.9 times higher in PfSPZ Vaccine recipients than PfSPZ-CVac recipients at time of CHMI. Vaccine efficacy at a median of 14 weeks after last PfSPZ-CVac dose was 55% (8 of 13, P = 0.051) and at a median of 15 weeks after last PfSPZ Vaccine dose was 27% (5 of 15, P = 0.32). The higher VE in PfSPZ-CVac recipients of 55% with a 27-fold lower dose was likely a result of later stage parasite maturation in the liver, leading to induction of cellular immunity against a greater quantity and broader array of antigens.

Publication types

  • Clinical Trial
  • Randomized Controlled Trial
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adolescent
  • Adult
  • Aged
  • Animals
  • Antibodies, Protozoan
  • Antimalarials / therapeutic use
  • Child
  • Child, Preschool
  • Chloroquine / therapeutic use
  • Double-Blind Method
  • Equatorial Guinea / epidemiology
  • Female
  • Humans
  • Immunization
  • Immunogenicity, Vaccine*
  • Infant
  • Malaria Vaccines / adverse effects
  • Malaria Vaccines / immunology*
  • Malaria, Falciparum / prevention & control*
  • Male
  • Middle Aged
  • Parasitemia
  • Plasmodium falciparum / immunology*
  • Vaccines, Attenuated / adverse effects
  • Vaccines, Attenuated / immunology
  • Young Adult

Substances

  • Antibodies, Protozoan
  • Antimalarials
  • Malaria Vaccines
  • Vaccines, Attenuated
  • Chloroquine