title: The role of age and exposure to Plasmodium falciparum in the rate of acquisition of naturally acquired immunity: a randomized controlled trial.
abstract: BACKGROUND
  The rate of acquisition of naturally acquired immunity (NAI) against malaria predominantly depends on transmission intensity and age, although disentangling the effects of these is difficult. We used chemoprophylaxis to selectively control exposure to P. falciparum during different periods in infancy and explore the effect of age in the build-up of NAI, measured as risk of clinical malaria.
  
  
  RESULTS
  A three-arm double-blind randomized placebo-controlled trial was conducted in 349 infants born to Mozambican HIV-negative women. The late exposure group (LEG) received monthly Sulfadoxine-Pyrimethamine (SP) plus Artesunate (AS) from 2.5-4.5 months of age and monthly placebo from 5.5-9.5 months; the early exposure group (EEG) received placebo from 2.5-4.5 months and SP+AS from 5.5-9.5 months; and the control group (CG) received placebo from 2.5-9.5 months. Active and passive case detection (PCD) were conducted from birth to 10.5 and 24 months respectively. The primary endpoint was time to first or only episode of malaria in the second year detected by PCD. The incidence of malaria during the second year was of 0.50, 0.51 and 0.35 episodes/PYAR in the LEG, EEG and CG respectively (p = 0.379 for the adjusted comparison of the 3 groups). The hazard ratio of the adjusted comparison between the LEG and the CG was 1.38 (0.83-2.28, p = 0.642) and that between the EEG and the CG was 1.35 (0.81-2.24, p = 0.743).
  
  
  CONCLUSIONS
  After considerably interfering with exposure during the first year of life, there was a trend towards a higher risk of malaria in the second year in children who had received chemoprophylaxis, but there was no significant rebound. No evidence was found that the age of first exposure to malaria affects the rate of acquisition of NAI. Thus, the timing of administration of antimalarial interventions like malaria vaccines during infancy does not appear to be a critical determinant.
  
  
  BACKGROUND
  ClinicalTrials.gov NCT00231452.
authors.affiliation: Centre de Recerca en Salut Internacional de Barcelona (CRESIB), Hospital Clínic-Universitat de Barcelona, Barcelona, Spain. caterina.guinovart@cresib.cat
authors.forename: Caterina
authors.initials: C
authors.lastname: Guinovart
authors.forename: Carlota
authors.initials: C
authors.lastname: Dobaño
authors.forename: Quique
authors.initials: Q
authors.lastname: Bassat
authors.forename: Augusto
authors.initials: A
authors.lastname: Nhabomba
authors.forename: Llorenç
authors.initials: L
authors.lastname: Quintó
authors.forename: Maria Nélia
authors.initials: MN
authors.lastname: Manaca
authors.forename: Ruth
authors.initials: R
authors.lastname: Aguilar
authors.forename: Mauricio H
authors.initials: MH
authors.lastname: Rodríguez
authors.forename: Arnoldo
authors.initials: A
authors.lastname: Barbosa
authors.forename: John J
authors.initials: JJ
authors.lastname: Aponte
authors.forename: Alfredo G
authors.initials: AG
authors.lastname: Mayor
authors.forename: Montse
authors.initials: M
authors.lastname: Renom
authors.forename: Cinta
authors.initials: C
authors.lastname: Moraleda
authors.forename: David J
authors.initials: DJ
authors.lastname: Roberts
authors.forename: Evelin
authors.initials: E
authors.lastname: Schwarzer
authors.forename: Peter N
authors.initials: PN
authors.lastname: Le Souëf
authors.forename: Louis
authors.initials: L
authors.lastname: Schofield
authors.forename: Chetan E
authors.initials: CE
authors.lastname: Chitnis
authors.forename: Denise L
authors.initials: DL
authors.lastname: Doolan
authors.forename: Pedro L
authors.initials: PL
authors.lastname: Alonso
mesh_terms: D056704:Adaptive Immunity; D000367:Age Factors; D000962:Antimalarials / Q000627:therapeutic use; D018890:Chemoprevention; D002675:Child, Preschool; D005260:Female; D006801:Humans; D015994:Incidence; D007223:Infant; D053208:Kaplan-Meier Estimate; D016778:Malaria, Falciparum / Q000453:epidemiology / Q000276:immunology* / Q000517:prevention & control; D008297:Male; D010963:Plasmodium falciparum / Q000276:immunology*; D015995:Prevalence
chemical_list: D000962:Antimalarials