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Insights into long-lasting protection induced by RTS,S/AS02A malaria vaccine: Further results from a phase IIb trial in Mozambican children

Guinovart, Caterina, Aponte, John J., Sacarlal, Jahit, Aide, Pedro, Leach, Amanda J., Bassat, Quique, Macete, Eusebio, Dobano, Carlota, Lievens, Marc, Loucq, Christian, Ballou, W. Ripley, Cohen, Joe and Alonso, Pedro L. (2009). Insights into long-lasting protection induced by RTS,S/AS02A malaria vaccine: Further results from a phase IIb trial in Mozambican children. PLoS One,4(4):e5165-1-e5165-8.

Document type: Journal Article
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IRMA ID 75039815xPUB512
Title Insights into long-lasting protection induced by RTS,S/AS02A malaria vaccine: Further results from a phase IIb trial in Mozambican children
Author Guinovart, Caterina
Aponte, John J.
Sacarlal, Jahit
Aide, Pedro
Leach, Amanda J.
Bassat, Quique
Macete, Eusebio
Dobano, Carlota
Lievens, Marc
Loucq, Christian
Ballou, W. Ripley
Cohen, Joe
Alonso, Pedro L.
Journal Name PLoS One
Publication Date 2009
Volume Number 4
Issue Number 4
ISSN 1932-6203   (check CDU catalogue  open catalogue search in new window)
Scopus ID 2-s2.0-65349096887
Start Page e5165-1
End Page e5165-8
Total Pages 8
Place of Publication United States
Publisher Public Library of Science
HERDC Category C1 - Journal Article (DIISR)
Abstract Background:
The pre-erythrocytic malaria vaccine RTS,S/AS02A has shown to confer protection against clinical malaria for at least 21 months in a trial in Mozambican children. Efficacy varied between different endpoints, such as parasitaemia or clinical malaria; however the underlying mechanisms that determine efficacy and its duration remain unknown. We performed a new, exploratory analysis to explore differences in the duration of protection among participants to better understand the protection afforded by RTS,S.

Methodology/Principal Findings:
The study was a Phase IIb double-blind, randomized controlled trial in 2022 children aged 1 to 4 years. The trial was designed with two cohorts to estimate vaccine efficacy against two different endpoints: clinical malaria (cohort 1) and infection (cohort 2). Participants were randomly allocated to receive three doses of RTS,S/AS02A or control vaccines. We did a retrospective, unplanned sub-analysis of cohort 2 data using information collected for safety through the health facility-based passive case detection system. Vaccine efficacy against clinical malaria was estimated over the first six-month surveillance period (double-blind phase) and over the following 12 months (single-blind phase), and analysis was per-protocol. Adjusted vaccine efficacy against first clinical malaria episodes in cohort 2 was of 35.4% (95% CI 4.5–56.3; p = 0.029) over the double-blind phase and of 9.0% (−30.6–36.6; p = 0.609) during the single-blind phase.

Conclusions/Significance:
Contrary to observations in cohort 1, where efficacy against clinical malaria did not wane over time, in cohort 2 the efficacy decreases with time. We hypothesize that this reduced duration of protection is a result of the early diagnosis and treatment of infections in cohort 2 participants, preventing sufficient exposure to asexual-stage antigens. On the other hand, the long-term protection against clinical disease observed in cohort 1 may be a consequence of a prolonged exposure to low-dose blood-stage asexual parasitaemia.
DOI http://dx.doi.org/10.1371/journal.pone.0005165   (check subscription with CDU E-Gateway service for CDU Staff and Students  check subscription with CDU E-Gateway in new window)


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