Responses to 2009 H1N1 vaccine in children 3 to 17 years of age

To the Editor: The current 2009 pandemic influenza A (H1N1) virus is associated with substantial morbidity in children, with 45% of hospitalizations occurring in patients under 18 years of age.1 One possible reason for this trend is a lack of preexisting immunity against the 2009 H1N1 virus among children.2 Experience with other pandemic vaccines has suggested that two doses of vaccine for children and adults would be needed to meet the licensure criteria of the Center for Biologics Evaluation and Research (CBER).3 According to these criteria, the lower bound of the two-sided 95% confidence interval should meet or exceed 40% . . .