Twelve years of pneumococcal conjugate vaccination in the Netherlands: Impact on incidence and clinical outcomes of invasive pneumococcal disease.

INTRODUCTION: In 2006, the Netherlands introduced the 7-valent pneumococcal conjugate vaccine (PCV7) in their national immunisation programme. In 2011, PCV7 was replaced by the 10-valent vaccine (PCV10). We report on the impact of PCV on invasive pneumococcal disease (IPD) incidence, clinical syndromes and patient outcomes. METHODS: Pneumococcal isolates of hospitalised IPD patients between June 2004 and May 2018 were obtained from nine sentinel laboratories, covering 25% of the Dutch population. All isolates were serotyped. IPD incidence and clinical outcome were determined before and after introduction of PCV7 and after the switch to PCV10, stratified by age and serotype. RESULTS: Compared to before PCV7 introduction, significant declines in IPD incidence were observed in 2016-2018 in children <5 years (69%), 18-49 year olds (31%) and ≥65 year olds (19%). Compared to before PCV10 introduction, the IPD incidence in 2016-2018 declined in children <5 years (RR:0.68, 95%CI:0.42-1.11), 5-17 year olds (RR:0.58, 95%CI:0.29-1.14) and 18-49 year olds (RR:0.72, 95%CI:0.57-0.90), but not in 50-64 year olds (RR:0.94, 95%CI:0.81-1.10) and ≥65 year olds (RR:1.04, 95%CI:0.0.93-1.15). While the case fatality rate (CFR) decreased from 16.2% pre-PCV to 13.4% post-PCV10 (RR:0.83, 95%CI:0.70-0.99), the switch to PCV10 had no further impact on CFR (RR:1.14, 95%CI:0.96-1.36). CONCLUSION: Twelve years of PCV in the Netherlands has resulted in a sustained reduction of IPD incidence in children and younger adults. The switch from PCV7 to PCV10 did not have additional impact on the IPD incidence in older adults and CFR due to emerging non-vaccine serotypes.