{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2025,10,23]],"date-time":"2025-10-23T11:25:35Z","timestamp":1761218735446,"version":"build-2065373602"},"reference-count":44,"publisher":"MDPI AG","issue":"6","license":[{"start":{"date-parts":[[2025,6,12]],"date-time":"2025-06-12T00:00:00Z","timestamp":1749686400000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"Ministry of Education and Science, Bulgaria, Scientific Research Fund","award":["KP-06-H43\/4-30.11.2020"],"award-info":[{"award-number":["KP-06-H43\/4-30.11.2020"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Vaccines"],"abstract":"<jats:p>Introduction: An effective vaccination strategy requires monitoring serotype changes by geography and age. This study analyzed Streptococcus pneumoniae serotypes in healthy children under 6 years of age vaccinated with PCV10 in Bulgaria from October 2021 to May 2025. Methods: A total of 569 children were screened for the lytA and cpsA genes viareal-time polymerase chain reaction (real-time PCR). Positive samples were typed using relevant kits, and 76 serotypes\/serogroups of S. pneumoniae were identified. Results: Nasopharyngeal swabs from 232 children (40.8%) were found to carry S. pneumoniae, and a total of 255 serotypes were detected, with 19B\/19C (17.2%), 6C (10.7%), and 15B\/15C (9.8%) being the most prevalent. Of these, 91 serotypes (15.9%) were included in at least one vaccine, while the remaining 164 serotypes (25.4%) were not. The carriage rate reduced to 22% in 2023 but increased to 47% in 2024. Overall, younger children had lower carriage rates (p &lt; 0.05), with serotype 6C being more common in children under 12 months of age (25%). Approximately 9.1% of pneumococcal carriage cases involved co-detected serotypes, with significantly higher co-detection rates for 19B\/19C, 15B\/15C, 10B, 10F\/C, 23B, 7C\/40, 23A, and 24A compared with mono-detection rates (p &lt; 0.05). Conclusions: 19B\/19C, 6C, 15B\/15C, and 19A were identified as the main serotypes. Children over 3 years of age were also more likely to carry multiple pneumococci. These findings emphasize the need to reassess childhood vaccination strategies to curb the spread of antibiotic-resistant serotypes.<\/jats:p>","DOI":"10.3390\/vaccines13060634","type":"journal-article","created":{"date-parts":[[2025,6,12]],"date-time":"2025-06-12T03:59:17Z","timestamp":1749700757000},"page":"634","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":1,"title":["Impact of the National Vaccination Strategy on the Prevalence of Streptococcus pneumoniae and Its Serotypes Among Clinically Healthy Children Under Six Years of Age During and After the COVID-19 Pandemic"],"prefix":"10.3390","volume":"13","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-4543-6831","authenticated-orcid":false,"given":"Ivelina","family":"Trifonova","sequence":"first","affiliation":[{"name":"National Centre of Infectious and Parasitic Diseases, 26 Yanko Sakazov Blvd., 1504 Sofia, Bulgaria"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-4975-4340","authenticated-orcid":false,"given":"Victoria","family":"Levterova","sequence":"additional","affiliation":[{"name":"National Centre of Infectious and Parasitic Diseases, 26 Yanko Sakazov Blvd., 1504 Sofia, Bulgaria"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Ivan","family":"Simeonovski","sequence":"additional","affiliation":[{"name":"National Centre of Infectious and Parasitic Diseases, 26 Yanko Sakazov Blvd., 1504 Sofia, Bulgaria"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Magi","family":"Ivanova","sequence":"additional","affiliation":[{"name":"National Centre of Infectious and Parasitic Diseases, 26 Yanko Sakazov Blvd., 1504 Sofia, Bulgaria"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Nadia","family":"Brankova","sequence":"additional","affiliation":[{"name":"National Centre of Infectious and Parasitic Diseases, 26 Yanko Sakazov Blvd., 1504 Sofia, Bulgaria"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Todor","family":"Kantardzhiev","sequence":"additional","affiliation":[{"name":"National Centre of Infectious and Parasitic Diseases, 26 Yanko Sakazov Blvd., 1504 Sofia, Bulgaria"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2025,6,12]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"355","DOI":"10.1038\/s41579-018-0001-8","article-title":"Streptococcus pneumoniae: Transmission, colonization and invasion","volume":"16","author":"Weiser","year":"2018","journal-title":"Nat. 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