Elsevier

Vaccine

Volume 17, Issues 23–24, 6 August 1999, Pages 2946-2950
Vaccine

Hepatitis B vaccination in infancy in The Gambia: protection: against carriage at 9 years of age

https://doi.org/10.1016/S0264-410X(99)00178-4Get rights and content

Abstract

To estimate the efficacy in The Gambia (West Africa) of infant hepatitis B vaccination against infection and carriage with the virus at the age of 9 years. The HBV status of 9-year old children vaccinated in infancy was compared to that of unvaccinated children of the same age. Eight percent of the vaccinated children had been infected by HBV compared to 50% of the unvaccinated control group; HBV carrier status was 0.6 and 10% respectively, resulting in a vaccine efficacy of 83% against infection and of 95% against chronic carriage. The results show that infant vaccination provides a high level of protection at the age of nine years against both HBV infection and chronic carrier status and no booster dose of vaccine is required in the first decade. These findings support the WHO recommendation for the introduction of HBV vaccination into the Expanded Programme on Immunization in Africa.

Introduction

In sub-Saharan Africa, hepatitis B virus (HBV) infection is endemic, with 15–20% of the adult population being chronic carriers. Persistent hepatitis B infection is also responsible for more than 60% of hepatocellular carcinoma (HCC), which is the major cause of cancer mortality in males in this continent, with cases occurring as early as adolescence [1], [2]. The most effective way to prevent HBV-associated acute and chronic liver diseases, including HCC, is vaccination at a population level. Hepatitis B vaccine became available in 1982 and the impact of such a vaccination programme is being assessed in The Gambia.

The Gambia Hepatitis Intervention Study (GHIS) was initiated in 1986 and consisted of the progressive introduction of hepatitis B vaccine into the routine immunization services of The Gambia up to 1990, since when it has been routinely offered to all newborn children in the country. The aims of the GHIS were: firstly to evaluate in a randomized trial the protection provided by HBV vaccination administered during the first year of life against subsequent HBV primary infection, the development of chronic carriage status and primary liver cancer, and secondly to demonstrate that the introduction of HBV vaccination into the EPI was logistically feasible and effective in Africa. We report here the results of the GHIS 9 years after its inception.

HBV vaccination trials were also initiated in the late 1980s in south-east Asia [3], [4]. The transmission of HBV infection in these regions differs from that in Africa; in Asia perinatal transmission from mothers positive for HBV e antigen is frequent [5] whereas in Africa horizontal transmission (sibling-to-sibling) predominates [6]. Thus, the complementary studies in the Gambia and these other regions should provide valuable insights into the strategies for effective introduction of HBV vaccination in different populations of the world.

Section snippets

Subjects

The details, the methods of recruitment of the children and the logistics of the introduction of HB vaccine into the national Expanded Programme on Immunization (EPI) in the Gambia have been described previously [7], [8]. Briefly, the HBV vaccination, using Merck Sharp & Dohme plasma-derived vaccine, was progressively introduced from July 1986 until national coverage was achieved in February 1990. These four zones comprised the western peri-urban area of the country (zone 1), the central area

Results

Table 1a, Table 1b, Table 2 show the prevalence of HBV infection and HBV carriage in children of 9 years of age, who did or did not receive HBV vaccination during the first year of their life.

Discussion

The results reported here show that protection against HBV chronic carriage, following infant vaccination, is over 90% at 9 years of age. Even if the loss to follow-up of some known carriers is taken into account, the estimate remains at 90%. The risk of carriage given infection is known to be particularly high in the first 5 years of life [12] so the major period of risk for this cohort has passed. Thus although breakthrough infections increased from 5% at the age of 4 to 8% at 9 years (see

Acknowledgments

The Gambia Hepatitis Intervention Study is a collaborative project between the International Agency for Research on Cancer, the Government of the Republic of The Gambia and the Medical Research Council (UK). The project is supported by grants from the Direzione Generale per la Cooperazione allo Sviluppo of the Ministry of Foreign Affairs in Italy, the Regione Autonoma della Valle d’Aosta, Italy and the Medical Research Council of Sweden.

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