Effects of PCV10 and PCV13 on pneumococcal serotype 6C disease, carriage, and antimicrobial resistance

Background: The cross-protection of pneumococcal conjugate vaccines (PCV) against serotype 6C is not clearly documented, although 6C represents a substantial burden of pneumococcal disease in recent years. A systematic review by the World Health Organization that covered studies through 2016 concluded that available data were insufficient to determine if either PCV10 (which contains serotype 6B but not 6A) or PCV13 (containing serotype 6A and 6B) conferred protection against 6C. Methods: We performed a systematic review of randomized controlled trials and observational studies published between January 2010 - August 2022 (Medline/Embase), covering the direct, indirect, and overall effect of PCV10 and PCV13 against 6C invasive pneumococcal disease (IPD), non-IPD, nasopharyngeal carriage (NPC), and antimicrobial resistance (AMR). Results: Of 2548 publications identified, 112 were included. Direct vaccine effectiveness against 6C IPD in children ranged between 70 and 85 % for >= 1 dose PCV13 (n = 3 studies), was 94 % in fully PCV13 vaccinated children (n = 2), and -14 % for >= 1 dose of PCV10 (n = 1). Compared to PCV7, PCV13 efficacy against 6C NPC in children was 66 % (n = 1). Serotype 6C IPD rates or NPC prevalence declined post-PCV13 in most studies in children (n = 5/6) and almost half of studies in adults (n = 5/11), while it increased post-PCV10 for IPD and nonIPD in all studies (n = 6/6). Changes in AMR prevalence were inconsistent. Conclusions: In contrast to PCV10, PCV13 vaccination consistently protected against 6C IPD and NPC in children, and provided some level of indirect protection to adults, supporting that serotype 6A but not 6B provides crossprotection to 6C. Vaccine policy makers and regulators should consider the effects of serotype 6A-containing PCVs against serotype 6C disease in their decisions.