Farah RA and Sayad AE
Dept of Pediatrics, Rizk Hospital, Beirut, Lebanon

Objective: Children with cancer are at high risk of exposure to hepatitis B virus (HBV) infection because of their frequent need for blood products during treatment with chemotherapy. Protection of children with malignancies against HBV infection is not well-documented particularly in developing countries and optimal dosing and schedule of the vaccine is not fully established. We aimed to study the rates of HBV immunization among children with cancer at the time of diagnosis and the response of these patients to HBV vaccination.
Methods:  All children <16 yrs of age diagnosed with cancer at our institution between January 1999 and March 2001 were eligible.  A history of HBV vaccination via review of the immunization record and HbsAg and antiHBs antibody titers were obtained on all patients at diagnosis or shortly thereafter. Patients who had no history of immunization and/or hepatitis B antibody titers below 10 IU/l at the time of diagnosis received 3 doses of the vaccine.  Antibody levels were tested one month after each dose. A fourth dose was given if antibody levels remained non-protective after 3 doses of the vaccine. 
Results:  Twenty-seven patients with a mean age of 5.3 yr (range 1-16 yr) were eligible. Ten had leukemia, three had lymphoma and fourteen had solid tumors. Nine patients had a documented history of hepatitis B immunization prior to diagnosis and received between 1 and 4 doses of the recombinant DNA vaccine 10 ug/dose.  Among those who were immunized, 3 (33%) had antiHBs antibody levels below 10 IU/l although several reports have shown a seroconversion rate of 96% in healthy children. The six other patients had antibody levels between 33 and 1000 IU/l.  Response to vaccination while undergoing chemotherapy treatment will be presented at the meeting. 
Conclusion: A history of hepatitis B immunization in children with cancer is not a reliable indicator of protection against HBV as some children seem to loose their immunity at the time of diagnosis. Antibody titers need to be checked at diagnosis in this patient population and hepatitis B vaccine will need to be given for those who have non protective antibody levels.  The vaccine is safe and effective in children undergoing chemotherapy although few require a fourth dose of the vaccine in order to develop protective antibody titers.