Introduction of pneumococcal conjugate vaccine into the public immunization program in South Africa: translating research into policy

Abstract

In April 2009, South Africa was the first African country to introduce pneumococcal polysaccharide-protein conjugate vaccine (PCV) into its public immunization program. This review summarizes studies on pneumococcal epidemiology and PCV undertaken in South Africa, which contributed to the process of advocating for the inclusion of PCV into the public immunization program. Surveillance prior to the introduction of 7-valent PCV (PCV-7) indicated that 70% (418/593) of invasive pneumococcal disease (IPD) in infants, the age-group at highest risk of IPD, was attributable to PCV-7 serotypes. Furthermore, 65% of all IPD in children under-5 years was associated with underlying HIV infection. Initial immunogenicity studies reported that PCV vaccination of antiretroviral-naïve HIV-infected children was associated with lower geometric mean antibody concentrations and proportion with a serotype-specific antibody concentration above the putative threshold (≥0.35 μg/ml) of protection for IPD for some of the serotypes. The functionality of antibody induced by PCV in HIV-infected infants was inferior to that of HIV-uninfected infants. Vaccine efficacy of 9-valent PCV in a trial from South Africa reported an 83% reduction of vaccine-serotype IPD in HIV-uninfected children in the first two years of life, with protection persisting thereafter. However, vaccine efficacy against vaccine-serotype IPD declined from 65% at 2.3 years of age to 39% by six years of age in antiretroviral-naïve HIV-infected children. Based on the observation that a two-dose primary series of PCV during infancy resulted in similar immunogenicity compared to a three-dose schedule, as well as similar impact on nasopharyngeal colonization and effectiveness against IPD in HIV-uninfected children, the South African immunization program adopted a two-dose primary series with a booster dose at 9 months of age. This schedule was largely premised on containing the cost of vaccine introduction, whilst including a booster dose of PCV to assist in prolonging the duration of protection in HIV-infected children.