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- Title
A combined analysis of immunogenicity, antibody kinetics and vaccine efficacy from phase 2 trials of the RTS,S malaria vaccine.
- Authors
White, Michael; Bejon, Philip; Olotu, Ally; Griffin, Jamie; Bojang, Kalifa; Lusingu, John; Salim, Nahya; Abdulla, Salim; Otsyula, Nekoye; Agnandji, Selidji; Lell, Bertrand; Asante, Kwaku; Owusu-Agyei, Seth; Mahama, Emmanuel; Agbenyega, Tsiri; Ansong, Daniel; Sacarlal, Jahit; Aponte, John; Ghani, Azra
- Abstract
Background The RTS,S malaria vaccine is currently undergoing phase 3 trials. High vaccine-induced antibody titres to the circumsporozoite protein (CSP) antigen have been associated with protection from infection and episodes of clinical malaria. Methods Using data from 5,144 participants in nine phase 2 trials, we explore predictors of vaccine immunogenicity (anti-CSP antibody titres), decay in antibody titres, and the association between antibody titres and clinical outcomes. We use empirically-observed relationships between these factors to predict vaccine efficacy in a range of scenarios. Results Vaccine-induced anti-CSP antibody titres were significantly associated with age (P = 0.04), adjuvant (P <0.001), pre-vaccination anti-hepatitis B surface antigen titres (P = 0.005) and pre-vaccination anti-CSP titres (P <0.001). Co-administration with other vaccines reduced anti-CSP antibody titres although not significantly (P = 0.095). Antibody titres showed a biphasic decay over time with an initial rapid decay in the first three months and a second slower decay over the next three to four years. Antibody titres were significantly associated with protection, with a titre of 51 (95% Credible Interval (CrI): 29 to 85) ELISA units/ml (EU/mL) predicted to prevent 50% of infections in children. Vaccine efficacy was predicted to decline to zero over four years in a setting with entomological inoculation rate (EIR) = 20 infectious bites per year (ibpy). Over a five-year follow-up period at an EIR = 20 ibpy, we predict RTS,S will avert 1,782 cases per 1,000 vaccinated children, 1,452 cases per 1,000 vaccinated infants, and 887 cases per 1,000 infants when co-administered with expanded programme on immunisation (EPI) vaccines. Our main study limitations include an absence of vaccine-induced cellular immune responses and short duration of follow-up in some individuals. Conclusions Vaccine-induced anti-CSP antibody titres and transmission intensity can explain variations in observed vaccine efficacy.
- Subjects
MALARIA vaccines; VACCINE effectiveness; CIRCUMSPOROZOITE protein; IMMUNIZATION; CLINICAL trials; ANTIGENS
- Publication
BMC Medicine, 2014, Vol 12, Issue 1, p1
- ISSN
1741-7015
- Publication type
Article
- DOI
10.1186/s12916-014-0117-2