Impact of pneumococcal conjugate vaccination on acute otitis media incidence and severity in young children

From 2000 onwards, national childhood pneumococcal conjugate vaccination (PCV) has been introduced across the world to prevent invasive pneumococcal disease (IPD) and childhood pneumonia. Because Streptococcus pneumoniae (S. pneumoniae) is also one of the most common pathogens causing acute middle ear infections (acute otitis media; AOM), the preventive effects of PCV may be much more wide ranging: AOM is among the commonest childhood infections and a leading cause of antibiotic prescribing, specialist referrals and ENT surgery in children.
Early and dense colonisation of the nasopharynx with S. pneumoniae as well as pneumococcal AOM occurring in early life (early life AOM) have been associated with an increased risk for subsequent and more complex AOM episodes caused by nonvaccine serotypes and other otopathogens. This has led to the hypothesis that by reducing or eliminating nasopharyngeal colonisation of S. pneumoniae and preventing early life AOM by PCV in infancy, the pathogenic pathway of middle-ear mucosal damage, biofilm formation and the occurrence of chronic/recurrent otitis media can be prevented.
PCVs have, however, also been associated with a phenomenon called ‘replacement’, which is a shift in distribution of potential pathogenic bacteria in the nasopharynx from pneumococcal strains included in the vaccine (vaccine serotypes) towards nonvaccine pneumococcal serotypes and other bacteria. This phenomenon could erode the ‘net benefit’ of PCVs on overall AOM and therefore ongoing monitoring of the impact of PCVs on AOM incidence and severity is warranted. Recent and accurate estimates on the impact of PCV on childhood AOM are of utmost importance since cost-effectiveness of PCV is also driven by their potential capacity to prevent AOM.
Using routinely collected longitudinal electronic health records and health insurance data of children pre and post introduction of the 7-valent PCV (PCV7) and the 10-valent PCV (PCV10) in the Dutch National Immunisation Programme (NIP), this thesis aims to provide these important estimates.