PURPOSE:To explore the impact of pneumococcal conjugate vaccines (PCVs) in preventing childhood pneumonia in the United Kingdom. METHODS:We carried out a population-based study to assess the trend of all-cause pneumonia in children aged under 10 years between 2002 and 2012. Data were obtained from the IMS Disease Analyser, a primary care database in the United Kingdom. Three time periods were defined to estimate monthly incidence: pre-PCV7 (January 2002 to August 2006), post-PCV7 (September 2006 to March 2010), and post-PCV13 (April 2010 to December 2012). Interrupted time series analysis (ITS) was performed to assess any immediate change or gradual change in the monthly incidence of pneumonia between prevaccination and postvaccination introduction. RESULTS:A total of 4228 children with at least one all-cause pneumonia episode were identified. The overall annual incidence rate of all-cause pneumonia declined by 37% from 3.8 episodes/1000 person-years in 2002 to 2.4 episodes/1000 person-years in 2012. Results of ITS analyses indicated that the incidence did not decline immediately after the introduction of PCV7 and PCV13. The incidence declined gradually in children aged under 2 years (IRR = 0.98; 95% CI, 0.97-0.99) post PCV7 and levelled off during post PCV13 (IRR = 1.00; 95% CI, 0.99-1.02). No significant changes in incidence trend was observed in children aged 2 to 4 years (IRR = 0.86; 95% CI, 0.68-1.07) and 5 to 9 years (IRR = 0.92; 95% CI, 0.73-1.15) after PCV13 introduction. CONCLUSIONS:In the United Kingdom, the incidence of all-cause pneumonia in children under 2 years declined after the introduction of PCV7 and levelled off in the first 2 years of introduction of PCV13. Continual monitoring is warranted to assess the population impact of PCV13 in preventing childhood pneumonia in the long term.