Impact of the conjugate pneumococcal vaccine in Arkansas

Background: On the basis of the success of the early trials in the prevention of invasive pneumococcal disease in infants and children using a heptavalent conjugate pneumococcal vaccine, the American Academy of Pediatrics recommended in August 2000 that the vaccine be given concurrently with other childhood immunizations. Methods: Data concerning invasive pneumococcal infections from 1998-2000 were compared with 2001-2003 to assess the impact of the heptavalent pneumococcal conjugate vaccine in Arkansas. Basic demographic data were gathered as well as history of vaccination with the pneumococcal vaccine, underlying medical conditions, site of infection and morbidity and mortality. Pneumococcal isolates were serogrouped or serotyped and penicillin susceptibilities were obtained. Results: The incidence of invasive disease decreased from a high of 5.78/100,000 population to 3.02/100,000 population (P = 0.002). Although the percentage of White patients increased from 2001-2003, the overall incidence of disease did not change. The incidence of disease among Blacks fell from 20.5/100,000 population to 4.9/100,000 population. The greatest decrease of disease occurred in children 24 months of age or younger with the incidence rate falling from 44.2/100,00 population to 8.30/100,000 population (P < 0.02). The incidence among White children 24 months of age or younger fell from 19/100,000 population to 1.8/100,000 population, whereas that of Black children 24 months of age or younger declined from 164/100,000 to 35/100,000. From 1998 to 2000, 3.7/100 cases were from nonvaccine serogroups compared with 44/100 cases from 2001 to 2003 (P <0.001). In children 24 months of age or younger, the number of nonvaccine isolates increased from 1.3/100 cases to 30.5/100 cases (P <0.001). Overall 56 (44%) were nonsusceptible to penicillin from 1998 to 2000; that was not significantly different from 2001-2003 when 37 (46%) of 81 isolates were nonsusceptible to penicillin. Conclusions: A significant decrease of invasive pneumococcal disease has been documented in Arkansas. Of concern, however, is the increasing number of invasive isolates not included in the current vaccine.