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The influence of age on the development of the hepatitis B carrier state
W J Edmunds1, G F Medley, D J Nokes
1Department of Biology, Imperial College of Science, Technology and Medicine, London, U.K.
Insights
Infants infected with hepatitis B virus (HBV) perinatally have a high chance of becoming carriers. Early childhood immunization can significantly reduce new hepatitis B carriers.
Area of Science:
- Hepatology
- Virology
- Epidemiology
Background:
- Hepatitis B virus (HBV) infection can lead to a chronic carrier state.
- The age at which infection occurs is a critical factor in HBV persistence.
Purpose of the Study:
- To examine the relationship between age at HBV infection and the development of the carrier state.
- To model the probability of becoming an HBV carrier based on age at infection.
Main Methods:
- Analysis of published and unpublished survey data on HBV infection.
- Application of maximum likelihood estimation to fit an empirical model.
Main Results:
- A strong inverse correlation exists between age at HBV infection and carrier state probability.
- Perinatal HBV infection (infants < 6 months) results in a high carrier probability (0.885).
- Carrier probability sharply decreases with age, reaching approximately 0.1 in adulthood (>15 years).
Conclusions:
- Age at HBV infection is a key determinant of chronicity.
- Childhood immunization campaigns delaying infection age can substantially reduce new HBV carrier generation.
Abstract:
The relation between the age at infection with hepatitis B virus (HBV) and the development of the carrier state is examined by using data from a number of published and unpublished surveys. A remarkably consistent relation was found. Infants infected perinatally (within the first 6 months of life) were found to have a high probability of becoming carriers (0.885; 95% C.L. 0.84-0.93). Over the infant and early childhood age classes there was found to be a sharp decrease in the proportion of infections which lead to the carrier state. By adulthood (over 15 years) the probability of developing the carrier status was found to be about 0.1. A model was fitted to the data by using maximum likelihood, which provides a good empirical description of the observed data and can be used to predict the expected probability of developing the carrier state given the age at infection. It is postulated that, as a result of this rapid decline in the probability of becoming a carrier during early childhood, a mass childhood immunization campaign, which will tend to postpone the average age at infection in the unvaccinated community, will have a disproportionately large impact on the rate of generation of new carriers.