Global Vaccine Safety

Questions and answers

Revised September 2007

Q: Is hepatitis B vaccination associated with a risk for leukaemia?

A: No. Five studies have reviewed the risk of leukaemia following hepatitis B vaccination. The only suggestion of a potential association comes from the preliminary results from the Northern California Childhood Leukemia Study by Xiaomei Ma, Monique Does, Patricia A. Buffler, John K. Wiencke. The authors presented a poster at American Association for Cancer Research Annual Meeting, San Francisco, April 9, 2002. This study reports an epidemiological association between receipt of hepatitis B vaccine and childhood leukaemia in a group of 334 children in northern California. This is the first study to ever report such an association. In their presentation, the authors hypothesize that thiomersal, a mercury-containing preservative may be the cause of the association.

However, there is some evidence suggesting that hepatitis B vaccination does not cause childhood leukaemia. During the period 1991 to 1998, when the rate of hepatitis B vaccination in American 2-year-olds was climbing from zero to over 80%, there was no corresponding increase in childhood leukaemia. According to the National Cancer Institute, "Childhood leukemias appeared to increase in incidence in the early 1980s, with rate in the preceding years at fewer than 4 cases per 100,000. Rates in the succeeding years have shown no consistent upward or downward trend and have ranged from 3.7 to 4.8 cases per 100,000." National Cancer Institute Cancer Facts, 25 April, 2005 (http://cis.nci.nih.gov/fact/6_40.html).

Four additional studies in France, Germany and New Zealand do not indicate any link between hepatitis B vaccination or vaccination with thiomersal-containing vaccines and leukaemia.

Preliminary results from another US study do not show an association; it also suggests such studies must overcome a number of methodologic problems relating to differences in completeness of immunization history for cases and controls

Q: IS HEPATITIS B DISEASE OR INFECTION ASSOCIATED WITH LEUKAEMIA?

A: No such association has ever been reported.

Q: IS THERE EVIDENCE THAT MERCURY IS ASSOCIATED WITH LEUKAEMIA?

A: No. Outbreaks of leukaemia have not followed accidental exposure to large amounts of mercury, such as in Minamata, Japan and in Iraq. These exposures included pregnant women. Occupational exposure to mercury also has not been associated with leukaemia. The association of thiomersal containing hepatitis B vaccine and leukaemia is not biologically plausible as cancers associated with metal carcinogens involve continual or repeated doses before cancer reveals itself, whereas thiomersal contains ethyl mercury that is excreted rapidly from the body. Furthermore, hepatitis B vaccine is a very minor source of vaccine-associated mercury received by children in the U.S.

Q: IS THERE FURTHER RESEARCH BEING DONE ON THE RISK OF LEUKAEMIA FOLLOWING HEPATITIS B VACCINATION?

A: The authors of the most recent study reanalyzed their data (Ma X, Does MB, Metayer C, Russo C, Wong A, Buffler PA. Vaccination history and risk of childhood leukaemia. Int J Epidemiol; 34(5):1100-1109, 2005.). Other US researchers with access to a large database are also studying this research question. In addition this issue is still being investigated in France in the context of a wider study of risks factors for childhood cancers including leukaemia. The study results will be expected by mid-2004.

Q: Should parents continue to get their children vaccinated against hepatitis B?

A: Yes. The risks of hepatitis B remain. The study from California does not change the current WHO recommendations as clearly stated by the Global Advisory Committee on Vaccine Safety.

In their presentation, the authors of the California study have said,"Given the importance of hepatitis B vaccine in preventing hepatoma [liver cancer], especially in high risk populations such as infants born to hepatitis B surface antigen positive mothers, the known risks of serious disease outweigh the suspected risks suggested by this study..."

Page updated: 02 october 2008

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