Impact of pneumococcal conjugate vaccines on burden of invasive pneumococcal disease and serotype distribution of Streptococcus pneumoniae isolates: an overview from Kuwait.

Diseases caused by Streptococcus pneumoniae are a major worldwide public health problem. The seven-valent pneumococcal conjugate vaccine (PCV7) was introduced in Kuwait in August 2006 and the 13-valent vaccine, PCV13, in August 2010, for children aged <2 years, with catch-up programs for those from 2 to 5 years. The objective of this study was to evaluate the impact of vaccination on vaccine and non-vaccine serotype distribution in invasive and noninvasive S. pneumoniae isolates obtained in Kuwait from August 2006 through December 2011, as compared with previously published data. The susceptibility of all the isolates to penicillin was also evaluated. The study included all cases of noninvasive and invasive pneumococcal diseases (IPD) in children and adults among all age groups during this period. All isolates were serotyped using the Quellung reaction antisera and their susceptibility to penicillin was determined using the E test method. A total of 395 pneumococcal isolates were included in the study. After vaccine introduction, 23% of isolates were from children ≤5 years of age and 49% of cases in this age group were invasive, while 46% of isolates were from adults >50 years of age and 27% of cases in this age group were invasive. Two of 13 cerebrospinal fluid isolates and only one of 266 respiratory isolates obtained were penicillin resistant. For the post-vaccine period, the predominant serotypes in children ≤5 years were 19F, 19A, 6A, 8 and 15B for invasive isolates and 19F and 23F for noninvasive isolates and the predominant serotypes in adults >50 years of age were 14, 3, 1, 19F and 8 for invasive isolates and 19F, 23F, 6B, 14 and 19A for noninvasive isolates. Among children <2 years of age, coverage with PCV7, PCV10, and PCV13 was 34.6%, 38.5% and 61.5%, respectively, in the period post-vaccine introduction. Among children 2-5 years of age, corresponding coverage rates were 42.1%, 47.4% and 63.1%, respectively. A similar trend was noticed in adults, with coverage rates in the 51- to 65-years age group of 45.8%, 62.5% and 70.8% respectively. Compared with previously published findings, from the period prior to vaccine introduction, this represented an increased incidence in some non-PCV7 serotypes that are included in PCV13 (serotypes 1, 6A, and 3). In conclusion, with the emergence of new pneumococcal serotypes, broader vaccine coverage will aid in the prevention of IPD in children.