Invasive disease due to Haemophilus influenzae serotype b ten years after routine vaccination, South Africa, 2003-2009.

INTRODUCTION: South Africa started routine infant immunization against Haemophilus influenzae serotype b (Hib) disease in 1999 with an accelerated three-dose schedule of Hib conjugate vaccine (HibCV) without a booster dose. Following initial declines in Hib disease, national surveillance has identified increasing numbers of Hib disease episodes in fully vaccinated children.

MATERIALS AND METHODS: We reviewed national laboratory-based surveillance data from 2003 through 2009 for invasive Hib disease episodes among children <5 years, including HIV status and vaccination histories. We defined HibCV failures as invasive Hib disease in children at least four months of age who had received all recommended doses of HibCV.

RESULTS: Despite high HibCV vaccination coverage, detection rates of Hib disease in children <5 years increased from 0.7 per 100,000 population in 2003 to 1.3/100,000 in 2009 (p<0.001). Among 263 episodes of invasive Hib disease among children with known vaccination status, 135 (51%) were classified as vaccine failures. Of vaccine failures, 55% occurred among case patients ≥18 months old. HIV status was documented for 90 children with vaccine failure; 53% were not HIV infected.

DISCUSSION AND CONCLUSIONS: Vaccine failures, which occurred in both HIV-infected and -uninfected children, comprised half of the rise in invasive Hib disease detected in South African children 10 years after national introduction of Hib vaccine. These findings suggest that HibCV recommendations may require revision. In November 2010, children in South Africa began receiving a booster dose of HibCV as part of a pentavalent vaccine.