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Infection and Immunity, November 2004, p. 6586-6588, Vol. 72, No. 11
0019-9567/04/$08.00+0     DOI: 10.1128/IAI.72.11.6586-6588.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.

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

Do Gia Canh,1 Feng-ying (Kimi) Lin,2 Vu Dinh Thiem,1 Dang Duc Trach,1 Nguyen Dinh Trong,3 Nguyen Duc Mao,3 Steven Hunt,2 Rachel Schneerson,2 John B. Robbins,2 Chiayung Chu,2 Joseph Shiloach,4 Dolores A. Bryla,2 Marie-Claude Bonnet,5 Dominique Schulz,5 and Shousun C. Szu2*

Diarrhea Diseases Epidemiology and Field Research Section, National Institute of Hygiene & Epidemiology, Hanoi,1 Centre for Preventive Medicine, Phu Tho Province, Vietnam,3 National Institute of Child Health and Human Development,2 National Institute of Digestive, Diabetes, and Kidney Diseases, National Institutes of Health, Bethesda, Maryland,4 Aventis Pasteur, Lyon, France5

Received 17 June 2004/ Returned for modification 12 July 2004/ Accepted 15 July 2004

In a double-blind, randomized, and placebo-controlled previous trial, the efficacy of Vi-rEPA for typhoid fever in 2- to 5-year-olds was 89.0% for 46 months. Vi-rEPA 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-rEPA in this age group. Two doses of Vi-rEPA 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-rEPA used in this and previous trials.

* Corresponding author. Mailing address: National Institutes of Health, Building 31, Room 2A29, Bethesda, MD 20892-2324. Phone: (301) 496-4524. Fax: (301) 402-9108. E-mail: szus{at}mail.nih.gov.

{dagger} This article is dedicated with affection and admiration to the late Dang Duc Trach, Chairman of the Vietnam General Association of Medicine and Pharmacy and Director of the Extended Program on Immunization, Vietnam.

Editor: D. L. Burns

Infection and Immunity, November 2004, p. 6586-6588, Vol. 72, No. 11
0019-9567/04/$08.00+0     DOI: 10.1128/IAI.72.11.6586-6588.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.





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