Vaccination against Haemophilus influenzae type b in Sweden : Aspects of epidemiology, economy and the process of introduction

Sammanfattning: Since 1992-1993 vaccination against Haemophilus influenzae type b (Hib) with conjugated vaccines is included in the general Swedish childhood vaccination programme. In this thesis the introduction of Hib vaccination has been evaluated.The epidemiology and clinical spectrum of invasive H. influenzae disease was prospectively studied during the pre-vaccination period in a well-defined population of Sweden 1987-1992. The incidence (cases/100 000/personyear) was 5.9 for all ages and 55 in children 0 to 4 years of age. Serotype b was the dominating type, especially in children. Three patients died in connecting with illness and six developed permanent sequelae.In national studies, the incidence before and after introduction of the Hib vaccination programme was compared. The source for the studies was the report system from the clinical microbiology laboratories to the Swedish Institute of Infectious Disease Control. Already within one year after introduction a decreased incidence was observed. In the prevaccination period the incidence was 34 in 0 to 4 years old children. In 1998 the incidence had decreased to 1.6 in the same age group. Thirteen children were identified with invasive Hib disease in spite of vaccination. Effectiveness, which take in account both direct and indirect effects of vaccination in 0 to 4 years old children was calculated to 96.0% (95 %Cl, 94.2-97.4). To study the impact of Hib vaccination in the on the diagnosis epiglottitis a national register of all patients treated at Swedish hospitals was used. In the age group 0-4 year the incidence decreased with 95 % after introduction of Hib vaccination. Even in older ages a decrease was observed but this trend did not reach statistically significance.An evaluation of the economic consequences of a general childhood vaccination programme against Hib in Sweden was conducted. A retrospective prevaccination annual cohort of 0-4 year old children was compared with an annual cohort of the same age group after a completely implemented vaccination programme against Hib. The cost analysis shows that vaccination against Hib is cost saving when indirect costs are included in the analysis. In the cost-benefit analysis it is shown that society will gain -88 million Swedish Crowns annually when Hib vaccination is totally implemented.The process of introducing general childhood Hib vaccination was studied. The critical factors for implementation of the immunisation programme were found to be the vaccine product, conception of the disease, government economy and public decision-making. Five activity systems were found to be involved in the implementation process, the systems of vaccine production, government administration, news distribution, science, and disease prevention. To structure the results a theoretical framework was used, Culture Historical Activity Theory. The study shows that a broad range of aspects must be considered before an intervention such as a general vaccination programme can be implemented in society.