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Aim: Little data is available on pneumococcal serotypes and their antimicrobial resistance in the pneumococcal conjugate vaccination era in young children with acute otitis media (AOM). Here such data is provided from Slovakia, acountry with sequential introduction and parallel-use of the three commercially available pneumococcal conjugate vaccines (PCVs; PCV7; PCV13; PCV10)., Methods: This observational study takes advantage of the fact that tympanocentesis is the standard of care in children with AOM in Slovakia. Over the 12 year observation period, participating pediatric ENT specialists sent samples taken during tympanocentesis from children with AOM to their local MEDIRIX laboratories for identification of bacteria. Pneumcoccal isolates were serotyped and tested for antimicrobial resistance. Incidence data could be calculated from 1 region., Results: Study participation and completeness of typing increased over time. Based on testing of 1,131 isolates over 12 years, PCV7-serotypes rapidly waned after PCV7 introduction in 2009 and had virtually disappeared in 2014. The maximum fraction of PCV10-only isolates (1, 5, 7F) was 2.7 % (2009) whereas the additional 3 PCV-serotypes (3, 6A, 19A) in PCV13 represented the largest proportion of pneumococcal AOM cases as of 2010. This finding remained unchanged during the period of highest PCV10-market share (2012-2017) and even until the end of the observation period (2019). The fraction of untypeable pneumococci (<6 %) and non-PCV13-serotypes (16-34 %) increased 2012-2017, but decreased again thereafter. Serotype 19A evolved as the most relevant (multidrug-) resistant pneumococcal serotype, again particularly during the time with high sales of PCV10 (2012-2017). Incidence data from the Bratislava region document a huge impact of PCV use (77 % vaccine uptake: mainly PCV13) on AOM in children < 6 years. Serotypes 19A and 3 remain the only relevant pneumococcal serotypes in young Slovakian children with AOM., Conclusions: As AOM is one of the most common bacterial infections in children < 6 years, the observed benefits of PCVs in reducing vaccine serotypes have been tremendous. With sequential / parallel-use of PCVs, serotypes 3 and (MDR-) 19A today make the largest proportion (about 2/3) of pneumococcal AOM in Slovakia. This data will help to further guide the choice of pneumococcal conjugate vaccines for pediatricians and parents., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 The Author(s). Published by Elsevier Ltd.. All rights reserved.)