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Infection and Immunity, November 1999, p. 5806-5810, Vol. 67, No. 11
0019-9567/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.

Safety and Immunogenicity of Vi Conjugate Vaccines for Typhoid Fever in Adults, Teenagers, and 2- to 4-Year-Old Children in Vietnam

Zuzana Kossaczka,1 Feng-Ying C. Lin,1 Vô Anh Ho,2 Nguyen Thi Thanh Thuy,3 Phan Van Bay,2 Tran Cong Thanh,3 Ha Ba Khiem,3 Dang Duc Trach,4 Arthur Karpas,1 Steven Hunt,1 Dolores A. Bryla,1 Rachel Schneerson,1 John B. Robbins,1 and Shousun C. Szu1,*

National Institutes of Health, Bethesda, Maryland 20892,1 Huu Nghi Hospital, Cao Lânh District, Dong Thap Province,2 Pasteur Institut, Ho Chi Minh City,3 and National Institute of Hygiene and Epidemiology, Hanoi,4 People's Republic of Vietnam

Received 7 June 1999/Returned for modification 13 July 1999/Accepted 13 August 1999

The capsular polysaccharide of Salmonella typhi, Vi, is an essential virulence factor and a protective vaccine for people older than 5 years. The safety and immunogenicity of two investigational Vi conjugate vaccines were evaluated in adults, 5- to 14-year-old children, and 2- to 4-year-old children in Vietnam. The conjugates were prepared with Pseudomonas aeruginosa recombinant exoprotein A (rEPA) as the carrier, using either N-succinimidyl-3-(2-pyridyldithio)-propionate (SPDP; Vi-rEPA1) or adipic acid dihydrazide (ADH; Vi-rEPA2) as linkers. None of the recipients experienced a temperature of >38.5°C or significant local reactions. One injection of Vi-rEPA2 into adults elicited a geometric mean (GM) increase in anti-Vi immunoglobulin G (IgG) from 9.62 enzyme-linked immunosorbent assay units/ml (EU) to 465 EU at 6 weeks; this level fell to 119 EU after 26 weeks. In the 5- to 14-year-old children, anti-Vi IgG levels at 6 weeks elicited by Vi-rEPA2, Vi-rEPA1, and Vi were 169, 22.8, and 18.9 EU, respectively (P = 0.0001 for Vi-rEPA1 and Vi with respect to Vi-rEPA2). At 26 weeks, the anti-Vi IgG levels for recipients of Vi-rEPA2, Vi-rEPA1, and Vi were 30.0, 10.8, and 13.4 EU, respectively (P < 0.001 for Vi-rEPA1 and Vi with respect to Vi-rEPA2); all were higher than the preinjection levels (P = 0.0001). Vi-rEPA2 also elicited the highest anti-Vi IgM and IgA levels of the three vaccines. In the 2- to 4-year-old children at 6 weeks following the first injection, Vi-rEPA2 elicited an anti-Vi IgG level of 69.9 EU compared to 28.9 EU for Vi-rEPA1 (P = 0.0001). Reinjection increased Vi antibody levels from 69.9 to 95.4 EU for Vi-rEPA2 and from 28.9 to 83.0 EU for Vi-rEPA1. At 26 weeks, anti-Vi IgG levels remained higher than those at preinjection (30.6 versus 0.18 for Vi-rEPA2 and 12.8 versus 0.33 for Vi-rEPA1; P = 0.0001 for both). Vi vaccine is recommended for individuals of 5 years of age or older. In the present study, the GM level of anti-Vi IgG elicited by two injections of Vi-rEPA2 in the 2- to 4-year-old children was higher than that elicited by Vi in the 5- to 14-year-old children (30.6 versus 13.4; P = 0.0001). The safety and immunogenicity of the Vi-rEPA2 conjugate warrant further investigation.

* Corresponding author. Mailing address: National Institutes of Health, Bethesda, MD 20892. Phone: (301) 496-4524. Fax: (301) 402-9108. E-mail: scszu{at}helix.nih.gov.

Infection and Immunity, November 1999, p. 5806-5810, Vol. 67, No. 11
0019-9567/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.


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