Heptavalent-pneumococcal conjugate vaccine (Prevenar). Differences in effectiveness between populations

This article reviews the publications on the effectiveness of heptavalent-pneumococcal conjugate vaccine (PCV7) in the prevention of invasive pneumococcal disease (IPD) in children under five years of age. It also analyses the characteristics of the vaccine and its impact on the epidemiology of IPD in different places. Before the introduction of PCV7, the percentage of cases of IPD due to vaccine serogroups oscillated between 89% in the United States and 43% in Asia. In Spain it was 68%. Active laboratory-based surveillance shows that the introduction of PCV7 has had a highly variable impact on the incidence of IPD, with falls oscillating between 91% in the United States and 12% in Navarre, Spain. The global effectiveness of VNC7v in published studies varies between 31% and 89%, chiefly depending on the patterns of pneumococcal serotypes in each place. Numerous studies show a variable replacement capacity of the pneumococci, which means the effect of the vaccine can be reduced, as non-vaccine serotypes occupy the space left by the vaccine ones. A study in Navarre has found a risk of IPD due to non-vaccine serotypes that is 6 times higher in vaccinated children than in unvaccinated ones. In places where less than 70% of the serotypes that cause IPD are represented in the VNC7v, the effectiveness of its introduction in the vaccination will probably be slight and the routine vaccination schedule serotypes fast. In these cases, VNC7v could be reserved for children with IPD risk factors.