Various studies have found a high prevalence of antibodies to hepatitis A antigen in the serum

of patients with cancer [71] and [72], as well as a high incidence of HBV infection [73] and [74], which explains why hepatitis A and B vaccines should be considered. The two studies evaluating hepatitis A vaccine [75] and [76] Modulators mainly involved children with solid tumours on chemotherapy who received two doses separated by an interval of 6 months. The vaccine was found to be highly immunogenic and to have a good safety profile. One month after the second vaccine dose, antibody levels were protective in 24/27 patients (89%), two (7%) had borderline antibody levels, and only one Raf pathway (4%) did not show any antibody [75]. It has also been demonstrated

that the combined administration of hepatitis A and hepatitis B vaccines does not reduce the immunogenicity of hepatitis A vaccine or increase the risk of adverse events even in the presence of cancer [76]. Hepatitis B vaccine also seems to be immunogenic and safe, even when administered to oncological children on maintenance therapy [76], [77] and [78]. Meral et al. administered the second dose of the vaccine 1, 2 or 12 months after the first and, upon the completion of the vaccination schedule, anti-HB positivity was demonstrated in 94% of the children with solid tumours, out 90% of those with leukemia, and 74% of those with lymphoma [76]. Globally, 78% of the children developed find more protective antibody titres, and none of them was infected by HBV during the 3 years of follow-up; on the contrary, 10/26 children (39%)

who failed to respond to immunisation were infected [76]. Yetgin et al. [77] further demonstrated the efficacy of hepatitis B vaccine by showing that protection against HBV infection is possible in children with ALL even in the absence of specific antibodies after vaccination. They administered two booster doses to patients who had remained unresponsive to immunisation and obtained seroconversion in only 35.4%; however, the incidence of HBV infection was significantly lower in this group than in a similar group of non-immunised patients (7.5% vs 28.7%, p < 0.001). These findings suggest that the protective role of HBV vaccination is probably related to both humoral and cellular immunity [77]. Analysis of the available data regarding immune system function and the response to vaccines of children with cancer makes it possible to draw some conclusions as to how they can be protected against vaccine-preventable diseases. Table 2 summarises possible vaccination schedules suggested by the authors of this review on the basis of the available publications.