Methods: We carried out a population-based study to assess the trend of all-cause pneumonia in children aged <10 years between 2002 and 2012. Data were obtained from the IMS Disease Analyzer, a primary care database in UK. Three time-periods were defined to estimate monthly incidence: pre-PCV7 (January 2002–August 2006), post-PCV7 (September 2006–March 2010), and post-PCV13 (April 2010–December 2012). Interrupted time series analysis (ITS) was performed to assess any immediate change or gradual change in the monthly incidence of pneumonia between pre- and post-vaccination introduction. Results: A total of 4,228 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/1,000 person-years in 2002 to 2.4 episodes/1,000 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 <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 2-4 years (IRR=0.86; 95%CI=0.68-1.07) and 5-9 years (IRR=0.92; 95%CI=0.73-1.15) after PCV13 introduction. Conclusions: In the UK, the incidence of all-cause pneumonia in children <2 years declined after the introduction of PCV7 and levelled off in the first two years of introduction of PCV13. Continual monitoring is warranted to assess the population impact of PCV13 in preventing childhood pneumonia in the long-term.