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Effect of Dosage on Immunogenicity of a Vi Conjugate Vaccine Injected Twice into 2- to 5-Year-Old Vietnamese Children

2004; American Society for Microbiology; Volume: 72; Issue: 11 Linguagem: Inglês

10.1128/iai.72.11.6586-6588.2004

1098-5522

Do Gia Canh, Feng‐Ying C. Lin, Vũ Đình Thiểm, Dang Duc Trach, Nguyễn Đình Trọng, Nguyen Duc Mao, Steven Hunt, Rachel Schneerson, John B. Robbins, Chiayung Chu, Joseph Shiloach, Dolores A. Bryla, Marie-Claude Bonnet, Dominique Schulz, Shousun C. Szu,

Salmonella and Campylobacter epidemiology

ABSTRACT In a double-blind, randomized, and placebo-controlled previous trial, the efficacy of Vi- r EPA for typhoid fever in 2- to 5-year-olds was 89.0% for 46 months. Vi- r EPA contained 25 μg of Vi and induced a greater-than-eightfold rise in immunoglobulin G (IgG) anti-Vi in all of the vaccinees tested. In this investigation, we conducted a dosage-immunogenicity study of 5, 12.5, and 25 μg of Vi- r EPA in this age group. Two doses of Vi- r EPA were injected 6 weeks apart. Blood samples were taken before and at 10 weeks (4 weeks after the second injection) and 1 year later. All postimmunization geometric mean (GM) levels were higher than the preimmune levels ( P < 0.0001). At 10 weeks, the GM IgG anti-Vi level elicited by 25 μg (102 EU/ml) was higher than those elicited by 12.5 μg (74.7 EU/ml) and 5 μg (43 EU/ml) ( P < 0.004): all of the children had ≥3.52 EU/ml (estimated minimum protective level). One year later, the levels declined about sevenfold (13.3 and 11.3 versus 6.43 EU/ml, P < 0.0001) but remained significantly higher than the preimmune levels ( P < 0.0001), and >96% of the children had a greater-than-eightfold rise. This study also confirmed the safety and consistent immunogenicity of the four lots of Vi- r EPA used in this and previous trials.