Immunogenicity of the RTS,S/AS01 Malaria Vaccine and Implications for Duration of Vaccine Efficacy: Secondary Analysis of Data From a Phase 3 Randomised Controlled Trial

Lancet Infect Dis. 2015 Dec;15(12):1450-8. doi: 10.1016/S1473-3099(15)00239-X. Epub 2015 Sep 2.

Abstract

Background: The RTS,S/AS01 malaria vaccine targets the circumsporozoite protein, inducing antibodies associated with the prevention of Plasmodium falciparum infection. We assessed the association between anti-circumsporozoite antibody titres and the magnitude and duration of vaccine efficacy using data from a phase 3 trial done between 2009 and 2014.

Methods: Using data from 8922 African children aged 5-17 months and 6537 African infants aged 6-12 weeks at first vaccination, we analysed the determinants of immunogenicity after RTS,S/AS01 vaccination with or without a booster dose. We assessed the association between the incidence of clinical malaria and anti-circumsporozoite antibody titres using a model of anti-circumsporozoite antibody dynamics and the natural acquisition of protective immunity over time.

Findings: RTS,S/AS01-induced anti-circumsporozoite antibody titres were greater in children aged 5-17 months than in those aged 6-12 weeks. Pre-vaccination anti-circumsporozoite titres were associated with lower immunogenicity in children aged 6-12 weeks and higher immunogenicity in those aged 5-17 months. The immunogenicity of the booster dose was strongly associated with immunogenicity after primary vaccination. Anti-circumsporozoite titres wane according to a biphasic exponential distribution. In participants aged 5-17 months, the half-life of the short-lived component of the antibody response was 45 days (95% credible interval 42-48) and that of the long-lived component was 591 days (557-632). After primary vaccination 12% (11-13) of the response was estimated to be long-lived, rising to 30% (28-32%) after a booster dose. An anti-circumsporozoite antibody titre of 121 EU/mL (98-153) was estimated to prevent 50% of infections. Waning anti-circumsporozoite antibody titres predict the duration of efficacy against clinical malaria across different age categories and transmission intensities, and efficacy wanes more rapidly at higher transmission intensity.

Interpretation: Anti-circumsporozoite antibody titres are a surrogate of protection for the magnitude and duration of RTS,S/AS01 efficacy, with or without a booster dose, providing a valuable surrogate of effectiveness for new RTS,S formulations in the age groups considered.

Funding: UK Medical Research Council.

Publication types

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

MeSH terms

  • Antibodies, Protozoan / blood*
  • Female
  • Ghana
  • Humans
  • Immunization, Secondary
  • Incidence
  • Infant
  • Kenya
  • Malaria Vaccines / administration & dosage*
  • Malaria Vaccines / chemistry
  • Malaria Vaccines / immunology
  • Malaria, Falciparum / blood
  • Malaria, Falciparum / immunology
  • Malaria, Falciparum / parasitology
  • Malaria, Falciparum / prevention & control*
  • Male
  • Plasmodium falciparum / chemistry
  • Plasmodium falciparum / drug effects*
  • Plasmodium falciparum / immunology
  • Protozoan Proteins / antagonists & inhibitors*
  • Protozoan Proteins / chemistry
  • Protozoan Proteins / immunology
  • Tanzania
  • Treatment Outcome
  • Vaccination*
  • Vaccines, Subunit

Substances

  • Antibodies, Protozoan
  • Malaria Vaccines
  • Protozoan Proteins
  • Vaccines, Subunit
  • circumsporozoite protein, Protozoan