Continued control of pneumococcal disease in the UK – the impact of vaccination

Streptococcus pneumoniae, also known as the pneumococcus, is an important cause of morbidity and mortality in the developed and developing world. Pneumococcal conjugate vaccines were first introduced for routine use in the USA in 2000, although the seven-valent pneumococcal conjugate vaccine (PCV7) was not introduced into the UK’s routine childhood immunization programme until September 2006. After its introduction, a marked decrease in the incidence of pneumococcal disease was observed, both in the vaccinated and unvaccinated UK populations. However, pneumococci are highly diverse and serotype prevalence is dynamic. Conversely, PCV7 targets only a limited number of capsular types, which appears to confer a limited lifespan to the observed beneficial effects. Shifts in serotype distribution have been detected for both non-invasive and invasive disease reported since PCV7 introduction, both in the UK and elsewhere. The pneumococcal Haemophilus influenzae protein D conjugate vaccine (PHiD-CV, Synflorix; GlaxoSmithKline) and 13-valent pneumococcal conjugate vaccine (PCV13, Prevenar 13; Pfizer) have been newly licensed. The potential coverage of the 10- and 13-valent conjugate vaccines has also altered alongside serotype shifts. Nonetheless, the mechanism of how PCV7 has influenced serotype shift is not clear-cut as the epidemiology of serotype prevalence is complex. Other factors also influence prevalence and incidence of pneumococcal carriage and disease, such as pneumococcal diversity, levels of antibiotic use and the presence of risk groups. Continued surveillance and identification of factors influencing serotype distribution are essential to allow rational vaccine design, implementation and continued effective control of pneumococcal disease.