"The data available to date, although limited, does not demonstrate a causal association between HB immunization and CNS demyelinating diseases, including MS. No evidence presented at this meeting indicates a need to change public health policies with respect to HB immunization. Therefore, based on demonstrated important benefits - including the prevention of cirrhosis and cancer, and a hypothetical risk, the group supports the WHO recommendations that all countries should have universal infant and/or adolescent immunization programs and continue to immunize adults at increased risk of HB infection as appropriate."

Background:
Hepatitis B (HB) is one of the major diseases of mankind and is preventable with safe and effective vaccines. More than 2,000 million persons have serologic evidence of past or current HB virus infection and there are more than 350 million chronic carriers of the virus at high risk of death from cirrhosis and liver cancer, diseases which kill almost 1 million persons a year. HB vaccine has been available since 1982 and more than 1 thousand million doses have been used. HB vaccine has been considered one of the safest and least reactogenic vaccines. The vaccine is approximately 95% effective in preventing the HBV chronic carrier state, and direct reduction of liver cancer has already been documented in immunized children. Approximately 100 countries, consistent with World Health Organization policy, have added HB vaccination into their routine childhood immunization programmes and most countries have in addition a policy to vaccinate adults at increased risk. In recent years, several case reports have raised concern that HB immunization may be linked to new cases or reactivation of multiple sclerosis (MS) or other demyelinating diseases within a period of 2 to 3 months after vaccination. Since many countries use HB vaccine in their immunization program, a thorough scientific evaluation of these concerns was needed. The Viral Hepatitis Prevention Board, a World Health Organization Collaborating Centre for the prevention of viral hepatitis, therefore called a technical consultation on the safety of HB vaccines to review accumulated data and policy implications. This consultation took place in Geneva from September 28 through September 30, 1998 and brought together representatives from national public health and regulatory authorities, academia, the hospital sector, the pharmaceutical industry and the World Health Organization. Participants included experts in the fields of public health, epidemiology, immunology, neurology and pharmacology.

Participants were presented with data:

1. on the epidemiology of hepatitis B
2. on the epidemiology of multiple sclerosis
3. from national reporting systems of the USA, Italy, and Canada
4. from one active surveillance system using paediatric hospitals in Canada
5. from industry pharmaco-vigilance including post marketing surveillance and clinical studies
6. from published studies of hepatitis B safety
7. from a small number of recent and still unpublished analytic epidemiological studies conducted in France, the UK and the US (these were preliminary results).

The various theories used to explain a potential association between HB immunization and demyelinating diseases including MS in relation to biological plausibility were also discussed, particularly with respect to immunological theories. The group reviewed the epidemiology and current understanding of the pathogenesis of MS. Current understanding of these diseases indicates a multi-factorial pathogenesis and the contribution of both genetic and environmental factors. Numerous environmental factors including infectious agents have been evaluated in studies conducted throughout the world. Both the age distribution of onset of disease and migration studies suggest that exposure to an environmental agent in early childhood or adolescence contributes to the pathogenesis of MS with a 10-15 years interval to onset of disease. An increase in risk with increase in latitude has been consistently demonstrated, but this is a marker for an as yet unidentified factor. There are three hypotheses that could explain the observed cases of demyelinating following HB vaccine:

1. Coincidence, due to the large number of HB vaccine doses administered many of them in age groups where symptoms of MS first occur.

2. "Triggering": An increased risk of symptomatic demyelination following HB vaccine which would act as a "trigger" in individuals predisposed to develop MS or central nervous system (CNS) demyelinating diseases. These individuals would have developed demyelination with or without an altered natural history following some immunologic or other precipitating factor.

3. A true causal relationship between HB vaccination and MS or other CNS demyelinating disease.

 Evidence to support the first hypothesis includes the fact that no statistically significant association was found between hepatitis B vaccine and MS in the limited studies conducted to date. Further, the age and sex distributions of MS cases reported through spontaneous reporting systems match the recognised age and sex distribution of MS cases that preceded the use of the vaccine and are not correlated with vaccine administration. In support of the hypothesis of an increased risk of MS following HB vaccination seen as a precipitating factor is that some studies have shown slightly elevated odds ratios although these were not statistically significant. Evidence inconsistent with this hypothesis is the observation that no increased risk was found in another study. No tangible evidence was presented for the biologic plausibility of any association. There is no evidence whatsoever of a link between hepatitis B virus infection and CNS demyelinating disorders including multiple sclerosis. Additional epidemiological and immunological research is ongoing or planned to further examine any association between vaccination, including hepatitis B, and CNS demyelinating disease. Altogether, evidence in favour of an increased risk following vaccination is weak and does not meet the criteria for causality.

This page was last updated on August 08, 2012

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