Decreased prevalence of Moraxella catarrhalis in addition to Streptococcus pneumoniae in children with upper respiratory tract infection after introduction of conjugated pneumococcal vaccine – A retrospective cohort study

Abstract Objectives To study effects of the introduction of pneumococcal conjugate vaccines (PCV) on the interspecies dynamics of Streptococcus pneumoniae, Haemophilus influenzae and Moraxella catarrhalis in pre-school children with respiratory tract infection. Methods Nasopharyngeal samples from children aged ≤ 6 years with upper respiratory tract infection (n=14,473) in South Sweden were analysed during 14 consecutive years; 5 years prior to and 9 years following PCV introduction. The yearly prevalence was calculated, and multivariate count regressions between prevalence and estimated yearly proportions of vaccinated children were performed. Associations between pneumococcal serotypes and the other pathogens were assessed. Results When comparing the pre-vaccine period with the years following introduction, the prevalence of S. pneumoniae decreased by 65.5% (16.6 to 5.7 per 1,000 individuals; p Conclusions Following introduction of PCV, the prevalence of M. catarrhalis in addition to S. pneumoniae in children with respiratory tract infection decreased, also after adjusting for reduced numbers of samples taken. This may partly be attributed to a positive association between PCV serotypes and M. catarrhalis.