Efficacy of one or two doses of Ty21a Salmonella typhi vaccine in enteric-coated capsules in a controlled field trial. Chilean Typhoid Committee.
Typhoid fever remains an important public health problem in many areas of the world and an effective, non-reactogenic vaccine would be useful to control this disease. An attenuated Salmonella typhi strain (Ty21a), which has shown promise in previous trials, was evaluated in a controlled field trial in Santiago, Chile. In this trial, 82,543 schoolchildren were randomly assigned to receive one or two doses of Ty21a vaccine in enteric-coated capsules or placebo. The enteric-coated vaccine formulation was well tolerated and practical for mass oral immunization. In the first two years of surveillance, 213 cases of bacteriologically-confirmed typhoid fever were found in schoolchildren participating in the trial; annual rates in the placebo group were 139 and 227 per 100,000. Vaccine efficacy in the first two years after vaccination was 59% for two doses and 29% for one dose; no efficacy was found 3-5 years after vaccination. These results indicate that it will be necessary to identify a vaccine formulation and schedule for Ty21a S. typhi that is practical and provides high level protection for greater than 2 years.
Black
R E
RE
Center for Vaccine Development, University of Maryland School of Medicine, Baltimore.
Levine
M M
MM
Ferreccio
C
C
Clements
M L
ML
Lanata
C
C
Rooney
J
J
Germanier
R
R
D000284:Administration, Oral; D000293:Adolescent; D000328:Adult; D002648:Child; D004306:Dose-Response Relationship, Immunologic; D004311:Double-Blind Method; D006801:Humans; D007115:Immunization Schedule; D016032:Randomized Controlled Trials as Topic; D012485:Salmonella typhi / Q000276:immunology*; D014435:Typhoid Fever / Q000517:prevention & control*; D014436:Typhoid-Paratyphoid Vaccines / Q000008:administration & dosage; D014613:Vaccines, Attenuated / Q000008:administration & dosage
D014436:Typhoid-Paratyphoid Vaccines; D014613:Vaccines, Attenuated