Development and use of more than 25 child and adult vaccines since 1900 has had a substantial impact on global public health including elimination of smallpox and near elimination of diseases like polio and measles. Despite this success, introduction of new vaccine formulations, changing population demographics, and growing concerns about vaccine safety create the continued need for diverse and careful research about how vaccines affect individual and community health. The objective of this dissertation was to evaluate three questions relevant to the prevention of vaccine-preventable diseases.

In the first study, we estimated the effectiveness of measles vaccination in a cohort of 469,315 children born in the United Kingdom from 1994 to 2007, and evaluated the impact of decreasing population levels of measles vaccine coverage over time on the incidence of measles among children who were vaccinated. The results from this study affirm that measles vaccination greatly reduces the risk of measles, and indicate that decreasing rates of measles vaccination in the child population are associated with increasing measles incidence among appropriately vaccinated children.

In the second study, we identified 5,948 pneumonia cases and 23,123 controls from a population-based sample of elderly adults in the United Kingdom to evaluate the effectiveness of the currently recommended pneumococcal polysaccharide vaccine against pneumonia in this high risk group. After adjustment for underlying health status, we found a small protective effect of pneumococcal vaccination. We also observed evidence of effect measure modification whereby pneumococcal vaccination appeared to be more effective among elderly adults without prevalent comorbidities compared with those with one or more comorbid conditions.

In the third study, we used a cohort of 890,681 Danish children born between 1994 and 2007 to examine the association between child and maternal asthma and the incidence of childhood pneumococcal disease. We found a 2-fold increased rate of pneumococcal disease among children with asthma compared with children who did not have asthma. In addition, we found important biologic interaction between childhood asthma and comorbidity on the incidence of pneumococcal disease among older children. Together, results from these studies contribute important information about the epidemiology of vaccine-preventable diseases.