Reduction of Streptococcus pneumoniae in upper respiratory tract cultures and a decreased incidence of related acute otitis media following introduction of childhood pneumococcal conjugate vaccines in a Swedish county

Background: The effect of pneumococcal conjugate vaccines (PCV) on invasive pneumococcal disease is frequently reported, but the impact on upper respiratory tract infections in a clinical setting is less documented. Our aim in this 5-year observational study was to investigate serotype changes in a large number of Streptococcus pneumoniae upper respiratory tract isolates following sequential introduction of PCV7 and pneumococcal Haemophilus influenza protein D conjugate vaccine (PHiD-CV10) in a Swedish county. Methods: All bacterial isolates from the upper respiratory tract (nasopharynx, sinus or middle ear fluid) from patients with respiratory tract infections referred to a clinical microbiology laboratory prior to (2 years 2007-2008; n = 1566) and after introduction of PCV (3 years 2011-2013; n = 1707) were prospectively collected. Microbiological findings were compared between the two periods, and information from clinical referrals was recorded in order to explore changes in incidence of pneumococcal acute otitis media (AOM). Results: Pneumococcal serotypes covered by PHiD-CV10 decreased from 45 to 12 % prior to and after immunization (p < 0.001), respectively. Despite non-PHiD-CV10 serotypes increased from 49 to 80 %, a significant decline of 35 % in the absolute incidence of pneumocococal isolates (p < 0.001) was observed. Finally, the frequency of complicated AOM caused by S. pneumoniae decreased by 32 % (p < 0.001). Conclusions: After introduction of PCV in 2009, we have observed a significantly decreased number of pneumococcal isolates in the upper respiratory tract, a shift to non-PHiD-CV10 serotypes, and a reduction of complicated AOM. Our findings may have implications for future vaccine design.