Immune response to 2009 pandemic H1N1 influenza virus A monovalent vaccine in children with cancer

Abstract

Purpose: This study investigated the immune response to 2009 pandemic H1N1 influenza monovalent vaccine in children with cancer receiving chemotherapy. Methods: We enrolled 25 pediatric patients. Ten patients younger than 10 years old received two vaccinations and the remaining 15 patients older than 10 years old received one. We checked hemagglutination-inhibition (HAI) antibody titers in sera of patients before and 3-4 weeks after vaccination. Seroprotective titer was defined as HAI antibody titer ?40 and seroresponse as ?4-fold increase in HAI antibody titers after vaccination. Results: The pre- and post-vaccination seroprotective rates were 52% and 72% (P=0.24). Sixteen (64%) patients were possibly exposed to 2009 pandemic H1N1 influenza previously, and there was significant association between possible exposure and pre-vaccination seroprotective rate (P=0.03). Post-vaccination seroresponse rate was 32%, and seroresponse was greater in patients without pre-vaccination seroprotective titer than those with pre-vaccination seroprotective titer (50% vs. 15%, P=0.07). Children with lymphocyte counts above 1,500/μl during vaccination period had better seroresponse than those with lymphocyte counts below 1,500/μl (P=0.008). Post-vaccination geometric mean titer (GMT) significantly increased in patients younger than 10 years receiving two vaccinations (pre- and post-vaccination GMT were 21.4 and 60.6, respectively; P=0.025). Conclusions: Monovalent vaccine for the 2009 pandemic H1N1 influenza A was found to be partially immunogenic in children with cancer, as evidenced by 32% of seroresponse rate. Immune response can be improved with vaccinations administered to patients whose absolute lymphocyte counts returned to a level of 1,500/μl or higher. ? 2011 Wiley Periodicals, Inc.