Streptococcus pneumoniae carriage is often asymptomatic but can cause invasive pneumococcal disease. Pneumococcal carriage is a prerequisite for disease, with children as main reservoir and transmitters. Childhood carriage can therefore be used to determine which serotypes circulate in the population and which may cause disease in the non-vaccinated population. In 2006, a pneumococcal conjugate vaccine (PCV7) was introduced into the Norwegian Childhood Immunisation Programme, which was replaced by the more valent PCV13 in 2011. We investigated changes in pneumococcal carriage prevalence 4 years after switching to PCV13 compared to three previous surveys, and analysed factors associated with carriage in children.
We conducted a cross-sectional study in Norway, autumn 2015, among children attending day-care centres. We collected questionnaire data and nasopharyngeal swabs to identify pneumococcal serotypes. We compared the carriage prevalence in 2015 with surveys conducted in the same setting performed before widespread vaccination (2006; n?=?610), 2 years after PCV7 introduction (2008; n?=?600), and 2 years after switching to PCV13 (2013; n?=?874). Using multilevel logistic regression we determined the association between pneumococcal carriage and previously associated factors.
In 2015, 896 children participated, with age ranging from 8 to 80?months. The overall carriage prevalence was 48/100 children [95%CI 44-53] in 2015, 38% [29-46] lower than in 2006 pre-PCV7, and 23% [12-32] lower than in 2013, 2 years after switching to PCV13. The PCV13 carriage prevalence was 2.8/100 children [1.9-4.2] in 2015. Increasing age (p?