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

Since 1992-93 vaccination against Haemophilus influenzae type b (Hib) has b een included in the general Swedish childhood vaccination programme. The ai m of the present study is to describe the epidemiology, identify and descri be vaccine failures and calculate vaccine effectiveness during the first 6 y after introduction of vaccination against Hib. Laboratory reports of bloo d and cerebrospinal isolates to the Swedish Institute for Infectious Diseas e Control were used as the source for identifying the patients. Additional information was subsequently obtained from physicians and parents of childr en who had developed the disease during the study period. Vaccine failures were identified and vaccine effectiveness calculated. During the study peri od, 152 cases of invasive I-I. 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 va ccinated 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 93.2-97.5). The study supports earlier studies from several countries that conjugated H ib vaccination introduced in general childhood vaccination programs is effe ctive and substantially decreases Suffering from invasive Hib diseases.