2703. Pneumococcal Carriage of 13-Valent Pneumococcal Conjugate Vaccine (PCV13) and Non-PCV13 Serotypes among Greek Children Vaccinated with PCV13 in a 3 + 1 Schedule During the First 6 years after the Fourth Dose of PCV13

BACKGROUND: We evaluated the long-term impact of full PCV13 vaccination in a 3 + 1 schedule on pneumococcal colonization patterns of children in order to clarify PCV13 serotype persistence/enhancement and re-colonization. METHODS: From January 18 to August 29, 2017, consecutive children who had received the 4-dose course of PCV13, as per the National Immunization Program recommendations, were prospectively enrolled through 45 general pediatric practice facilities in 30 municipalities in Greece. A single oropharyngeal sample was obtained from each subject in a standardized manner (questionnaire, procedure). Based on the time interval since the fourth dose of PCV13, the children sampled were grouped for analysis in 6 groups: 26 days to 11 months; 12–23 months; 24–35 months; 36–47 months; 48–59 months, and 60–71 months. Carriage and distribution of Streptococcus pneumoniae serotypes was detected by RT–PCR. RESULTS: A total of 1212 children aged 14–83 months were investigated. S. pneumoniae was identified in the pharyngeal swab of 617 children (50.9%); 172/617 (27.9%) children carried > 1 pneumococcal serotypes. As a consequence of co-colonization, a total number of 718 S. pneumoniae (belonging to 28 serotypes) was identified. The carriage rate of non-PCV13 serotypes escalated within 3 years after the fourth dose and plateaued during the fourth and fifth year. The carriage rate of PCV13 serotypes escalated during the 4 years after the fourth dose and declined thereafter. 22/305 children (7.2%) carried one or more PCV13 serotypes in the first year after the fourth vaccine dose, 27/201 (13.4%) in the second year, 34/207 (16.4%) in the third year, 48/224 (21.4%) in the fourth year, 40/191 (20.9%) in the fifth year and 13/84 (15.5%) in the sixth year (P < 0.0001) (Figure 1). The colonization frequency of serotypes 3 and 19A increased with the rise of the vaccination time interval (Figure 2). Changes in the frequency of other PCV13 serotypes were not significant. Serotypes 7F, 14 and 23F were not recovered. CONCLUSION: Our study suggests that S. pneumoniae is present in the pharynx of children 26 days to 71 months after the completion of PCV13 vaccination, and that non-PCV13 serotypes predominate throughout this period. The carriage rate of PCV13 serotypes 3 and 19A increases significantly as the time interval from the fourth dose of PCV13 increases. [Image: see text] [Image: see text] DISCLOSURES: All authors: No reported disclosures.