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