Abstract
BackgroundThe pneumococcal conjugate vaccine PCV7 was introduced in Southwest Sweden in the child vaccination program in 2009, followed by PCV13 in 2010 and PCV10 in 2015. In this retrospective cohort study we assessed the pneumococcal serotype distribution in relation to predisposing factors, clinical manifestations and outcome during seven years after PCV introduction.MethodsClinical data from 1278 patients with 1304 episodes of invasive pneumococcal disease (IPD) between January 2009 and December 2015 in Region Västra Götaland, Sweden, were retrospectively collected from medical records. Pneumococcal isolates were serotyped by gel diffusion and/or Quellung reactions performed at the Public Health Agency in Sweden. Associations between serotypes and clinical characteristics were statistically evaluated by use of Fisher’s exact test, Mann-Whitney U test and Logistic regression analysis, whereas IPD episodes caused by serotypes over time were analyzed by Mantel-Haenszel chi-square test.ResultsWith the exception of serotype 3, the prevalence of PCV13 serotypes decreased during the study period, from 76% (n = 157) of all IPD episodes in 2009 to 25% (n = 42) in 2015 (p < 0.001) while non-PCV13 serotypes increased, mainly among patients ≥65 years and in patients with predisposing factors, including cardiovascular disease, pulmonary disease and malignancy (p < 0.001 for all). Patients with predisposing factors, including those with malignancy, immune deficiency or renal disease, were more likely to have IPD caused by a serotype not included in PCV13 rather than a vaccine-included serotype. Serotype 3 was associated with intensive care unit admissions while serotype 1 and 7F caused IPD among healthier and younger patients. PCV13 serotypes were associated with invasive pneumonia, and non-PCV13 serotypes were associated with bacteremia with unknown focus and with manifestations other than pneumonia or meningitis.ConclusionsNon-PCV13 serotypes caused the majority of IPD cases in Southwest Sweden, especially in patients ≥65 years and in patients with predisposing factors. Serotype 3, included in PCV13, was prevalent and often caused severe disease.
Highlights
Invasive pneumococcal disease (IPD) caused by the bacterium Streptococcus pneumoniae remains a major cause of morbidity and mortality despite the introduction of pneumococcal conjugate vaccines (PCVs) in the child vaccination programs worldwide [1].In January 2009, the conjugate vaccine PCV7 covering serotypes 4, 6B, 9 V, 14, 18C, 19F and 23F was offered to all children in Sweden at three, five and 12 months of age with no catch-up campaign for older children
Non-PCV13 serotypes caused the majority of IPD cases in Southwest Sweden, especially in patients ≥65 years and in patients with predisposing factors
No child below the age of five who had received all doses of the vaccine according to the child vaccination program, had IPD with a pneumococcal serotype included in the current vaccine
Summary
Invasive pneumococcal disease (IPD) caused by the bacterium Streptococcus pneumoniae remains a major cause of morbidity and mortality despite the introduction of pneumococcal conjugate vaccines (PCVs) in the child vaccination programs worldwide [1].In January 2009, the conjugate vaccine PCV7 covering serotypes 4, 6B, 9 V, 14, 18C, 19F and 23F was offered to all children in Sweden at three, five and 12 months of age with no catch-up campaign for older children. Through herd immunity, the incidence of IPD among unvaccinated adults has declined in many countries, an increase in non-vaccine serotypes has been observed [7,8,9]. The latter is attributable to the fact that non-vaccine serotypes have replaced vaccine serotypes as nasopharyngeal colonizers in preschool children [10]. The pneumococcal conjugate vaccine PCV7 was introduced in Southwest Sweden in the child vaccination program in 2009, followed by PCV13 in 2010 and PCV10 in 2015 In this retrospective cohort study we assessed the pneumococcal serotype distribution in relation to predisposing factors, clinical manifestations and outcome during seven years after PCV introduction
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