Epiglottitis in Sweden before and after introduction of vaccination against Haemophilus influenzae type b.

BACKGROUND: Acute epiglottitis is an important manifestation of invasive Haemophilus influenzae type b (Hib) infection. In 1992 and 1993 Hib vaccination was introduced in the general childhood vaccination program in Sweden. The aim of the present investigation was to study the impact of Hib vaccination on the diagnosis of epiglottitis in Sweden in children as well as adults. METHODS: A retrospective national population-based study on the incidence of epiglottitis in Sweden was performed for the 10-year period 1987 to 1996. The incidence calculations were based on figures from the national register of all patients treated at Swedish hospitals. The incidence (cases/100,000/year) for the prevaccination period 1987 to 1991 was compared with the incidence after Hib vaccination was introduced. RESULTS: In children a substantial decrease was found after introduction of large scale vaccination against Hib. Below 5 years of age the annual incidence decreased from 20.9 in 1987 to 0.9 in 1996. In adults a tendency toward a decrease in incidence was evident. CONCLUSIONS: Introduction of Hib vaccination in a general childhood program was followed not only by a >90% reduction in the incidence in the youngest age group but also by a reduction in the incidence in the older age groups and among adults.

Protective effect of breastfeeding on invasive Haemophilus influenzae infection: a case-control study in Swedish preschool children.

BACKGROUND: In Orebro County a 2.5-fold increase in the incidence of Haemophilus influenzae (HI) meningitis was found between 1970 and 1980, an observation that initiated the present study. MATERIALS AND METHODS: In order to search for associations between morbidity in invasive HI infection and possible risk factors, a case-control study was conducted over a 6-year period from 1987 to 1992, before general Hib vaccination was introduced in Sweden. Fifty-four cases with invasive HI infection 139 matched controls were studied for possible risk factors such as day-care outside the home, short duration of breastfeeding, passive smoking, low socioeconomic level of the household, many siblings in the family, allergy, frequent, infections, repeated antibiotic treatments and immunoglobulin deficiency. RESULTS: Multivariate analysis showed a significant association between invasive HI infection and two independent factors, i.e. short duration (< 13 weeks) of exclusive breastfeeding, odds ratio (OR) 3.79 (95% confidence interval [CI] 1.6-8.8) and history of frequent infections, OR 4.49 (95% CI : 1.0-21.0). For the age at onset 12 months or older, the associations were stronger, OR 7.79 (95% CI : 2.4-26.6) and 5.86 (95% CI : 1.1-30.6), respectively. When breastfeeding duration in weeks was analysed as a continuous variable the OR was 0.95 (95% CI : 0.92-0.99), indicating a decreased risk with each additional week. Increased OR were observed for other risk factors as well but not of the magnitude found for short duration of breastfeeding. DISCUSSION: The association of decreased risk for invasive HI infection and long duration of breastfeeding was persisting beyond the period of breastfeeding itself. This finding supports the hypothesis of a long-lasting protective effect of breastfeeding on the risk for invasive HI infection. CONCLUSION: A decreased risk for invasive HI infection with long duration of breastfeeding was found. Our results do have implications for strategies in breastfeeding promotion, especially in countries where Hib vaccination is too costly and not yet implemented.

Immunization against Haemophilus influenzae type b in Sweden--a study of the introduction process.

AIMS: To study the introduction of Haemophilus influenzae type b (Hib) vaccination in Sweden, and to identify factors promoting and inhibiting the process. METHODS: The introduction of general childhood vaccination against Hib in Sweden in 1992-93 was studied using the Cultural Historical Activity Theory as a theoretical framework. RESULTS: Five activity systems were found to be involved in the introduction process, the systems of vaccine production, government administration, news distribution, science, and disease prevention. The critical factors for introduction of the programme were found to be the vaccine product, conception of the disease, government economy and public decision-making. CONCLUSIONS: The results show that a broad range of non-biomedical aspects must be considered when a public health intervention such as a general vaccination programme is introduced.

Economic evaluation of general childhood vaccination against Haemophilus influenzae type b in Sweden.

The objective of the study was to evaluate the economic consequences of a general childhood vaccination programme against Haemophilus influenzae type b (Hib) in Sweden. A retrospective pre-vaccination annual cohort of 0-4-y-old children was compared with an annual cohort of the same age group after a complete implemented vaccination program 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 approximately 88 million Swedish Crowns (SEK) annually when Hib vaccination is totally implemented. In conclusion, general childhood Hib vaccination is a cost-effective public health intervention in Swedish society.

Invasive disease due to Haemophilus influenzae type b during the first six years of general vaccination of Swedish children.

Since 1992-93 vaccination against Haemophilus influenzae type b (Hib) has been included in the general Swedish childhood vaccination programme. The aim of the present study is to describe the epidemiology, identify and describe vaccine failures and calculate vaccine effectiveness during the first 6 y after introduction of vaccination against Hib. Laboratory reports of blood and cerebrospinal isolates to the Swedish Institute for Infectious Disease Control were used as the source for identifying the patients. Additional information was subsequently obtained from physicians and parents of children who had developed the disease during the study period. Vaccine failures were identified and vaccine effectiveness calculated. During the study period, 152 cases of invasive H. influenzae were identified in the age group 0-14 y. During the 6-y period, 6 true vaccine failures, 6 apparent vaccine failures and 1 possible vaccine failure were found in nearly two million vaccinated child-years. The effectiveness of the Hib vaccination in the birth cohort of children 1993 to 1997 in Sweden was calculated to be 96.1% (95% confidence interval 94.2-97.5). The study supports earlier studies from several countries that conjugated Hib vaccination introduced in general childhood vaccination programs is effective and substantially decreases suffering from invasive Hib diseases.

The impact of Haemophilus influenzae type b vaccination in Sweden.

The number of patients with meningitis and bacteremia due to Haemophilus influenzae was studied in Sweden over the period 1987-1994. Conjugated H. influenzae type b vaccines were introduced in Sweden in 1992, and all children born after December 31, 1992, were offered vaccination free of charge. A rapid decline of H. influenzae meningitis and bacteraemia was observed in the autumn of 1993, when the expected peak incidence failed to appear. In the prevaccination period 1987-1991, the average annual incidence (cases/100,000) was 34.4 in children aged 0-4 years. In 1994, the annual incidence fell to 3.5. No significant decline was observed in older children or adults. There was a 92% reduction in the number of meningitis cases and an 83% reduction in cases of bacteraemia. A similar decline was noted in 2 regions which followed different strategies for the introduction of the vaccination programme.

Invasive Haemophilus influenzae disease: epidemiology and clinical spectrum before large-scale H. influenzae type b vaccination.

In a prospective study between January 1987 and December 1992, 103 patients with invasive Haemophilus influenzae (Hi) infection were identified in a well-defined population before large-scale Haemophilus influenzae type b (Hib) vaccination was introduced. The incidence (case/100,000/year) of invasive Hi infection was 5.9 for the whole population, 55 for children 0-4 years old and as high as 2.8 for adults. Hib was the predominant cause of the infection (83 cases) in children but, in adults, 13/39 (30%) cases were caused by non-typable Hi and 6/39 (19%) by Hi serotype f. Three patients (3%) died and 6 (5.8%) suffered a permanent sequel from the infection. All patients with such a sequel had invasive Hib infection. No significant difference between patients 0-6 years old and matched controls regarding the frequency of subnormal serum levels of immunoglobulins was found.