Epidemiology of invasive Haemophilus influenzae serotype b disease following implementation of a booster vaccine dose in South Africa

Abstract

In 2000, before the introduction of the Haemophilus influenzae serotype b (Hib) vaccine, Hib was among the most commonly occurring invasive bacterial infections responsible for serious infections and deaths among children <5 years worldwide. After the introduction of the Haemophilus influenzae serotype b conjugate vaccine (HibCV), significant drops in the incidence of invasive Hib disease were seen globally as well as in South Africa. However, a resurgence in Hib disease prompted the introduction of the Hib vaccine booster (Hib_VB) in South Africa’s Expanded Programme on Immunization (EPI) schedule in 2009. Given that no study had been done yet to assess the impact of this Hib_VB, this secondary data analysis aimed to assess the trends in invasive Hib disease post introduction of the Hib_VB in South Africa. This was a cross-sectional study which used retrospective observational surveillance data of invasive Hib disease. A pre- and post-Hib_VB analysis, to look at the trends of invasive Hib disease incidence among children <5 years following the introduction of the Hib_VB, was done. A risk factor analysis was also carried out to assess the characteristics of children <5 years with invasive Hib versus non-typeable Haemophilus influenzae (NT Hi) disease. Based on the observations of this study, the pre- and post-Hib_VB analysis showed that there was a significant reduction in the incidence of invasive Hib disease from the pre- Hib_VB years 2006-2008 to each of the post-Hib_VB years 2013, 2014, 2015, 2016, 2017, 2018, and 2019. The reduction ranged from 55.1% (95% CI: 30.1-72.0) in 2013 to 75.9% (95% CI:58.1-87.8) in 2018 compared to 2006-2008 (p<0.001). It was also observed that there was a reduction in the incidence of Hib among infants too young to receive any Hib vaccine (<6 weeks). In conclusion, the Hib_VB was effective in further reducing the incidence of invasive Hib disease among children <5 years in South Africa. It is recommended that all children receive Hib vaccine doses on time to ensure protection of all vulnerable children.