ENHANCED SURVEILLANCE OF INVASIVE HAEMOPHILUS-INFLUENZAE DISEASE IN ENGLAND, 1990 TO 1996 - IMPACT OF CONJUGATE VACCINES

We report an enhanced prospective survey of invasive Haemophilus influ enzae infections that has defined the pattern of invasive disease in f ive English regions for 2 years before and 4 years after the introduct ion of the H. influenzae type b (Hib) vaccination program. During the prevaccination period the majority of cases of invasive H. influenzae were caused by type b; most (89%) of these infections occurred in chil dren <5 years of age and the most common presentation was meningitis. Since the introduction of routine immunization of infants with conjuga te Hib vaccine, there has been a 16-fold reduction in the annual attac k rate of invasive Hib disease recorded in children <5 years of age, T his reduction is of a magnitude similar to that observed in other coun tries with Hib vaccination programs. The number of infections caused b y non-type b H. influenzae has shown a small but progressive increase over the same period, emphasizing the need for continued surveillance. There was no increase in the number of infections caused by other ser otypes, Diagnostic category varied with both age and serotype but was not affected by vaccine introduction; meningitis was the most common p resentation overall but pneumonia and bacteremia were more common in a dults and with noncapsulated isolates.