Efficacy Trial of Vi Polysaccharide Vaccine against Typhoid Fever in South-Western China

By Yang, H. H.; Wu, C. G. et al. | Bulletin of the World Health Organization, July 2001 | Go to article overview

Efficacy Trial of Vi Polysaccharide Vaccine against Typhoid Fever in South-Western China


Yang, H. H., Wu, C. G., Xie, G. Z., Gu, Q. W., Wang, B. R., Wang, L. Y., Wang, H. F., Ding, Z. S., Yang, Y., Tan, W. S., Wang, W. Y., Wang, X. C., Qin, M., Wang, J. H., Tang, H. A., Jiang, X. M., Li, Y. H., Wang, M. L., Zhang, S. L., Li, G. L., Bulletin of the World Health Organization


Voir page 630 le resume en francais. En la pagina 630 figura un resumen en espanol.

Introduction

Typhoid fever is still an endemic infectious disease in some rural areas of China, especially in the south. The warm climate and the abundance of rice fields frequently promote outbreaks of the disease. For example, the annual typhoid incidence for school-aged children in Jiangsu and Guangxi provinces is approximately 50 cases per 100 000 population. The leading cause of enteric fever in many countries is Salmonella typhi, followed by S. typhimurium and S. paratyphi. The main factors contributing to endemic typhoid may be a lack of adequate sewage disposal and a lack of protected water supplies, and in many developed countries the provision of safe water supplies has controlled or even eliminated typhoid. In developing countries, however, national or international efforts to reduce typhoid by providing effective sewage treatment and clean water may be required for at least a decade. Thus, the intensive use of an effective and safe vaccine in developing countries, especially in children, will probably be necessary to reduce the incidence of typhoid fever in endemic areas.

In the 1980s, killed whole cell vaccine was used to control endemic typhoid. Although this vaccine was effective, its widespread use has been impeded by unpleasant local and systemic side-reactions. Since 1990, the National Institute for Control of Pharmaceutical and Biological Products (NICPBP) of China has organized six Institutes of Biological Products to study the production of an alternative vaccine against typhoid fever derived from Vi polysaccharide. In a pilot study, the safety and immunogenicity of Vi vaccine produced in China showed that it was effective and safe. A further field test of a single 30-[micro]g dose of Vi vaccine in 81 000 people in Jiangsu Province demonstrated a protective efficacy of 71% after 12 months. As a result, the Vi polysaccharide vaccine was licensed as an experimental vaccine in China. However, to issue a formal production license in China the efficacy of the vaccine needed to be field tested over longer periods in other highly endemic areas. In this paper, we report the findings of a 19-month randomized, double-blinded field trial conducted in a predominantly school-aged group in Guangxi Province, in which we tested the efficacy of a single 30-[micro]g dose of Vi polysaccharide vaccine.

Methods

Pilot study

A pilot study was conducted to compare the immunogenicity and safety of Vi polysaccharide vaccine with commercially produced, killed, whole cell typhoid vaccine. The study was performed in 585 students aged 15-20 years in Jiangsu Province (1). Participants were allocated to one of five groups, each of which received a single-dose regimen: group 1 (118 students) 20 [micro]g Vi vaccine hypodermically; group 2 (116 students) 30 [micro]g Vi vaccine hypodermically; group 3 (113 students) 30 [micro]g Vi vaccine intramuscularly; group 4 (118 students) 1.5 E/0.5 ml killed whole cell typhoid vaccine hypodermically; group 5 (120 students) 0.5 ml normal saline delivered hypodermically.

In group 2 (the high dose Vi vaccine group), only 3% of the subjects developed fever ([is greater than] 37.5 [degrees] C), or local reactions (erythema [is greater than] 1 cm), 24 hours after vaccination, and all symptoms resolved within 48 hours after vaccination. The geometric mean titre (GMT) of anti-Vi antibodies in group 2, assessed with enzyme-linked immunosorbent assay (ELISA), rose from 5.4 [micro]g/ml pre-vaccination to 50.2 [micro]g/ml one month after vaccination, and declined to 38.2 [micro]g/ml six months after vaccination. Ninety-two percent of group 2 participants achieved a [is greater than or equal to] 4 fold rise of anti-Vi antibodies over baseline one month after vaccination. In contrast, only 81% of group 1 and 88% of group 3 participants achieved such antibody titres, and 29. …

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