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Between 1991-1999, the Patient Episode Database for Wales (PEDW) was investigated and an association between influenza A viruses circulating in the community and demand for inpatient management of lower respiratory tract illness demonstrated r=0.73 a finding which supports influenza contributing significantly to the winter bed crises seen in the Welsh NHS in recent years. Once admitted to hospital, the clinical outcomes of influenza and pneumonia are poor the average length of the inpatient stay being 14 days with approximately one third of elderly and high-risk individuals dying during the inpatient period. To assess the effectiveness of the inactivated influenza vaccine in preventing such hospitalisations, a prospective case-control study was undertaken in Gwent, South East Wales during the winter of 1999-2000. After controlling for age, sex, chronic disease status, pneumococcal vaccine uptake, previous inpatient management and primary care consultations in an unconditional logistic model, the inactivated influenza vaccine was found to reduce admissions for acute respiratory illness significantly OR .30 (95% CI: .21 to .44 ) this translating to a 70% reduction in admissions. Furthermore, the risk of death once hospitalised was reduced by 75% in vaccinees OR .25 (95% CI:.l 1 to .60). Vaccination coverage in South East Wales during this season was poor and examination of the determinants of respiratory vaccine uptake suggests that the chronic medical conditions for which vaccination are recommended are not equally weighted. Vaccines appear to be targeted at individuals with chronic pulmonary disease, leaving many other high-risk groups, particularly individuals with cardiovascular disease vulnerable to influenza and its sequelae. Smokers were also significantly less likely to have received the influenza and pneumococcal vaccines, the OR's being .40 (95% CI: .27 to .57) and .57 (95% CI: .36 to .91) respectively. The widespread use of respiratory vaccines in elderly and identified high-risk groups has substantial resource implications for secondary care services in Wales. The review of the literature in Chapters 1 and 2 highlights a paucity of epidemiological data on the impact of influenza and pneumonia within a UK setting. Furthermore, the evidence base for influenza and pneumococcal vaccination, both of which are integral components of primary care prevention strategies, rests on observational studies conducted predominantly in North America. This thesis aims to draw together a number of studies to develop an epidemiological picture of individuals hospitalised with influenza and pneumonia during the 1990s in Wales. Furthermore, specific public health issues, such as the delivery and uptake of respiratory vaccines and the effectiveness of influenza vaccination are examined. The methodologies of the studies are outlined in chapter 3. In Chapter 4, trends of hospitalisations for influenza and pneumonia in Wales are examined and mean annual rates of hospitalisations for influenza, pneumococcal pneumonia and broad sub categories of pneumonia reported. The relationship between surveillance data reporting influenza like illness at primary care level and demand for inpatient management of lower respiratory tract illness is examined. The hypothesis that influenza contributes significantly to the winter bed crisis in the Welsh NHS is also investigated. Potential risk factors for and outcomes of hospitalisation due to influenza and pneumonia are also reported which subsequently inform the planning of the case control study outlined in Chapters 3 and 5. In addition, the missed opportunity for reducing the demand for inpatient management of vaccine preventable respiratory disease is assessed and determinants of influenza and pneumococcal vaccine uptake described. Finally, in Chapter 5, the effectiveness of the inactivated influenza vaccine in reducing admissions for respiratory disease during an influenza outbreak period is reported and the impact of increased acute respiratory admissions on a district general hospital in South East Wales described.