The impact of the 13-valent pneumococcal conjugate vaccine on pneumococcal carriage in the Community Acquired Pneumonia Immunization Trial in Adults (CAPiTA) Study

Background: The impact of pneumococcal conjugate vaccination on the prevalence of nasopharyngeal carriage with pneumococci and other bacteria in adults is unknown. The direct effects of the 13-valent pneumococcal conjugate vaccine (PCV13) in community dwelling older adults was investigated as part of the randomized controlled Community Acquired Pneumonia immunization Trial in Adults (CAPiTA). Methods: We determined the carriage of S. pneumoniae, S. aureus, H. influenzae, and M. catarrhalis before and at 6, 12 and 24 months post-vaccination using PCR-based methods and conventional cultures of naso- and oropharyngeal swabs in 1,006 PCV13-recipients and 1,005 controls. Serotyping of the 13 vaccine-type (VT) pneumococci was performed by PCR targeting capsular synthesis genes and quellung reaction of isolates. Findings: Before randomization and based on PCR, 339 of 1891 subjects had nasopharyngeal carriage with any pneumococci (17.9%), and 114 of 1891 subjects (6.0%) carried a VT-pneumococci. At six months post-vaccination, VT-pneumococcal carriage was significantly lower in PCV13-recipients than in the placebo-group (RR 0.53 95%CI: 0.35-0.80; p=0.04). There was no difference between the groups at 12 and 24 months post-vaccination. Carriage of non-VT-pneumococci, S. aureus, H. influenzae, and M. catarrhalis did not change between groups. Interpretations: In community-dwelling adults of 65 years and older, a single dose of PCV13 appears to elicit a small and temporary reduction in VT-carriage at 6 months post-vaccination. Neither replacement by non-vaccine serotypes nor impact on other nasopharyngeal bacteria was observed