Effect of the introduction of pneumococcal conjugate vaccines on serotype prevalence in Kuwait and Saudi Arabia

Background: Streptococcus pneumoniae infection is a major cause of morbidity and mortality. Although pneumococcal disease burden in Kuwait and Saudi Arabia is considered high, comprehensive surveillance data on pneumococcal conjugate vaccine (PCV) effects are lacking. Methods: Sterile isolates from patients in Kuwait (2003-2016) and Saudi Arabia (aged <= 5 years, 2000-2010; all patients, 2011-2015) were included. Serotyped isolates were classified by inclusion in the 7-valent (PCV7) or 13-valent PCV (PCV13); isolates of other serotypes were classified as "non-PCV13". Isolate frequency (number of isolates/year) and classification of isolates according to vaccine type were assessed by period (before PCV, after PCV7, and after PCV13 introduction). Results: In Kuwait, the frequency of collected isolates was highest after PCV7 introduction. Decreased frequency of PCV7 serotypes was seen after PCV13 introduction compared with before PCV and after PCV7 introduction. Increased frequency of the 6 additional serotypes in PCV13 and non-PCV13 serotypes was observed after PCV7 introduction with a subsequent decrease in the 6 additional serotypes in PCV13 and non-PCV13 serotypes after PCV13 introduction. The percentage of isolates of vaccine serotypes in Kuwait decreased over time. In Saudi Arabia, the frequency of collected isolates was highest after PCV7 introduction. An increased frequency of PCV7 serotypes was observed after PCV7 introduction, with a further decrease after PCV13 introduction. For the 6 additional serotypes in PCV13, an increased frequency was seen after PCV7 and PCV13 introduction compared to before PCV introduction. For non-PCV13 serotypes, an increased frequency was observed after PCV13 introduction compared to after PCV7 introduction. The percentage of isolates covered by PCV13 serotypes was similar across periods, while a substantial decrease in isolates covered by PCV7 was seen after PCV13 introduction. Conclusion: PCVs in Kuwait and Saudi Arabia resulted in decreased frequency of some vaccine serotypes and an emergence of some non-PCV13 serotypes. Further investigation is warranted. (C) 2018 Elsevier Ltd. All rights reserved.