Haemophilus influenzae type b disease and vaccine booster dose deferral, United States, 1998-2009.

BACKGROUND Since the introduction of effective vaccines, the incidence of invasive Haemophilus influenzae type b (Hib) disease among children <5 years of age has decreased by 99% in the United States. In response to a limited vaccine supply that began in 2007, Hib booster doses were deferred for 18 months. METHODS We reviewed national passive and active surveillance (demographic and serotype) and vaccination status data for invasive H. influenzae disease in children aged <5 years before (1998-2007) and during (2008-2009) the vaccine shortage years to assess the impact of the vaccine deferral on Hib disease. We estimated the average annual number of Hib cases misclassified as unknown (not completed or missing) serotype. RESULTS From 1998 to 2007 and 2008 to 2009, the annual average incidence of Hib disease per 100000 population was 0.2 and 0.18, respectively; no significant difference in incidence was found by age group, gender, or race. Among Hib cases in both time periods, most were unvaccinated or too young to have received Hib vaccine. During 2001 to 2009, there were <53 Hib cases per year, with an estimated 6 to 12 Hib cases misclassified as unknown serotype. CONCLUSIONS The booster deferral did not have a significant impact on the burden of invasive Hib disease in children <5 years of age. Continued surveillance and serotype data are important to monitor changes in Hib incidence, especially during vaccine deferrals. Hib booster deferral is a reasonable short-term approach to a Hib vaccine shortage.