Pandemic (H1N1) 2009 vaccine in paediatric oncology patients: one dose or two doses?
Although the clinical course of pandemic (2009) H1N1 infection in paediatric oncology patients is, in general, not severe, it frequently results in delay in anti-cancer therapy, which may affect the long-term outcome of these patients (Caselli et al, 2010; Cheng et al, 2010). Moreover, Launes et al (2010) showed that children who received intensive chemotherapy could develop severe disease. Children always have an important role in transmission of influenza infection, annual vaccination remains the most effective way to offer protection in paediatric oncology patients and haematopoietic stem cell transplant recipients (Tramontana et al, 2010). Lu et al (2010) evaluated the immune response of a novel vaccine for H1N1 in healthy Chinese children. Three weeks after the first dose, 50% of children aged 3–9 years had acquired protective antibodies. After second dose of vaccine, protective antibody level was detected in 90% of subjects. Seroconversion rate was about 80% in this age group after two doses of vaccine (Lu et al, 2010). Data on the immunogenicity of this vaccine in paediatric oncology population is not available. Our group evaluated the immune response to pandemic (H1N1) 2009 vaccine in 12 oncology patients who were either on maintenance chemotherapy or had completed intensive chemotherapy within the last 12 months (median age 5Æ2 years, range 2Æ9–9Æ4 years). Written consents were obtained from parents and/or patients before enrolment to study. Ethical approval was obtained from the local institutional ethics committee. Two doses of inactivated pandemic (H1N1) 2009 vaccines (Panenza , Sanofi Pasteur, France) were administered intramuscularly 4 weeks apart. This is a non-adjuvant vaccine formulated to contain 15 lg haemagglutinin (HA) of influenza A/California/07/2009 (H1N1)-like virus. We evaluated the H1N1 antibody titres at baseline (TP0); 4 weeks after the first dose (TP1), and 4 weeks after second dose (TP2). The antibody titres were determined by a microneutralization assay using standard methods (Greenberg et al, 2009). The immunogenicity profiles included the seroprotection rate (the proportion of subjects with antibody levels of 1:40 or more), seroconversion rate (the proportion of subjects with a pre-vaccination antibody titre <1:40 and a post-vaccination titre ‡1:40 or a pre-vaccination titre ‡1:40 and an increase in the titre by a factor of four or more) were assessed. The clinical characteristics and results are shown in Table I. Before vaccination, 75Æ0% of subjects had a neutralizing antibody titre <1:40. At 4 weeks after first dose of vaccine, the seroprotection rate was 58Æ3% (7 out of 12 participants) of