Tuesday, May 4, 2010

Vaccination Against Hepatitis B Prevents Liver Cancer

As reported in the New York Times, San Francisco has launched an important public health campaign to promote vaccination against the hepatitis B virus which causes liver disease and liver cancer (story). This campaign is important for several reasons. Infection is usually silent and the impact on disease is many years after initial infection.

Prevention programs for cancer take different durations for the benefit to be observed. Vaccination programs offer one insight to the time frame of intervention and the ultimate reduction in cancer incidence. For cervical cancer prevention with human papilloma virus (HPV) vaccine, the current U.S. Center for Disease Control (CDC) recommends vaccination for women between ages 13 and 26; the benefit of this prevention will be observed many years hence. Hepatitis vaccination programs in Africa and Asia offer further illustration of these points. In the Gambia, a program launched in 1986 aims to evaluate the effectiveness of childhood vaccination with hepatitis B and current estimates are that the final outcome of reduced hepatocellular carcinoma in adults should be measurable from 2017 onwards. In Asia with nationwide hepatitis B vaccination implemented in Taiwan in 1984, results at 10 years show significant reduction in hepatocellular carcinoma in children. Clearly many years of follow-up are required to demonstrate protection of adults, though this outcome is implied by results to date.

The etiology of some 18 per cent of cancers worldwide can be linked to chronic infections due to agents such as Helicobacter pylori, human papillomaviruses (HPV), Hepatitis B, Hepatitis C, Epstein-Barr virus (EBV), human immunodeficiency virus (HIV), human herpes virus 8 (HHV-8), and Schistosoma haematobium, with the proportion of all cancer due to infections being much higher in developing countries (26 per cent, compared to 7.7 per cent in developed countries). The current burden of cancer in the developing world is dominated by infection, once smoking is accounted for. Of 10.8 million new cases of cancer worldwide (2002 figures), those caused by infectious agents are estimated as: H. pylori 5.5 per cent (mainly stomach, and lymphoma); HPV 5.2 per cent (mainly cervix, and ano-genital, mouth, pharynx); HBV and HBC 4.9 per cent (liver); EBV 1.0 per cent (nasopharynx, Hodgkin lymphoma and Burkitt lymphoma), HIV and HHV-8 0.9 per cent (Kaposi sarcoma, non-Hodgkin lymphoma) and other less common agents including schistosomes, HTLV-1, and liver flukes, less than 0.5 per cent. More than 25 per cent of cancer incidence in developing countries could be avoided if infectious causes of cancer were prevented. Successful vaccination programs have the potential to reduce cancer incidence and mortality; for example, Taiwan’s HBV vaccination program was initiated in 1984, and impressively high coverage rates (up to 97 per cent in 2004) have led to a consistent decline in hepatocellular cancer rates. However, a recent study by Chang et al. underscores the importance of a multi-pronged approach. Though Taiwan has seen a decrease in the incidence of hepatocellular cancer in children since initiation of the vaccination program (from 0.54 to 0.20 per 100,000 before and after the program), vertical transmission, vaccine failure, and the lack of hepatitis B immunoglobulin injection has affected program effectiveness and public health impact.

Given the burden of infection with the virus in Asian Americans in California, estimated at 10% it is not too early to begin a major campaign such as that instituted in San Francisco.

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