Background: Since many pathogens colonize the child's oro/nasopharynx in a similar manner, elimination of diseases such as those caused by Haemophilus influenzae type b (Hib) has a potential of augmenting other serious infections. Streptococcus pneumoniae is an agent of special interest now that Hib conjugates have been used widely for more than 2 decades.
Patients and Methods: All blood and cerebrospinal fluid isolations of Hib and S. pneumoniae were collected prospectively from 85,000 Finnish children at age 0–15 years by one central laboratory during 27 years.
Results: Hib vaccination, launched in 1986–1988, led to a quick decline of cases until the last was detected in 1991. In the next few years, the incidence of bacteremic S. pneumoniae infections increased, but now for 15 years, the numbers of cases have been slowly declining. This finding is not explained by less active sample-taking because the number of blood cultures have almost doubled in the past years.
Conclusions: Large-scale Hib vaccination does not increase the incidence of pneumococcal diseases which continue their year-to-year fluctuation at low levels. Only a years-long follow-up permits conclusions on a vaccination's potential influence on the epidemiology of other diseases.