Dissertation (MSc Paediatric Nursing)Background: This study, was intended to assess the population based impact of PCV, on the prevention of pneumonia among children aged 2 – 5 years in Zanzibar. Methods: A matched case control study of 560 random selected children was conducted in three regions with seven districts in Zanzibar from April to end of June 2018, controls were matched to the cases based on age and sex of the children with ratio 1:3 making a sample of 140 cases and 420 controls. Purposively sampling technique was used to select regions with districts, based on high prevalence of pneumonia and low uptake. Shehias were selected by using simple random sampling by lottery method. Systematic random sampling was used to select households. Pneumonia cases were verified by diagnosed clinician’s treatments charts as defined by the Integrated Management of Childhood illnesses (IMCI), PCV was verified by RCH card number one. Participants were interviewed through an interviewer structured questionnaires. Both descriptive and inferential analysis, was conducted by using SPSS. Results: Out of 560 children (57.1%) were male in the cases group. The mean age in both group were 3.46 and (SD = 1.076). 86.7% of them were immunized of whom 80.4% were completed, 4.5% incomplete three doses and 13.4% were not. After adjusted for confounders, factors associated with the uptake of PCV delivery at healthy facility, (AOR=2.328, 95%CI: 1.219; 4.445. Impact of PCV, findings have shown that 84.5% of the immunized children were free from pneumonia at the time of study (p <0.05). First to the fourth born children were significantly suffering from pneumonia (AOR=5.806; 95%CI: 1.477; 22.823). Conclusion: Full vaccination as per recommended schedule, had a significant success to better health as well pneumonia preventions. Pneumonia for under five children is still problem existing in Zanzibar. Other measures should be done to overcome this problem.