Starting in 2000, pneumococcal conjugate vaccine was licensed for use in young children. Controlled trials of the vaccine before nationwide release showed that it was highly effective in reducing the incidence of invasive pneumococcal disease when given in a four-dose regimen. Whitney and associates from the Centers for Disease Control and Prevention (CDC) offer an initial glimpse at national data on changes in the incidence of invasive pneumococcal disease since the vaccine was introduced.

Data were derived from the CDC's Active Bacterial Core Surveillance system from January 1996 through December 2001. The system tracks disease rates in a variety of metropolitan areas across the country for a population of about 16 million persons. More than 400,000 of these persons are children younger than two years, the target group for prevention of invasive pneumococcal disease. Invasive disease was defined as a positive culture for Streptococcus pneumoniae in any normally sterile body fluid (e.g., blood, cerebrospinal fluid).

Among children younger than two years, the baseline rate of invasive pneumococcal disease before vaccination was commonplace was 188 cases per 100,000 persons. This rate declined to 59 cases per 100,000 persons after about one year of widespread vaccine use, a decrease of approximately 69 percent from baseline. Within the overall decreased rate of invasive disease, cases caused by the seven pneumococcal serotypes included in the vaccine dropped by 78 percent, while a nonsignificant rise occurred in cases caused by nonvaccine serotypes. Similar declines for invasive disease were observed among black children (73 percent) and white children (62 percent). Interestingly, the rates of invasive disease also declined for age groups outside the target population of children younger than two years. Among children younger than five years, there was a 59 percent decline in rates of invasive disease. Even adult populations showed reduced rates of invasive disease, with 32 percent fewer cases in persons 20 to 39 years, 8 percent less disease in those 40 to 64 years, and an 18 percent reduction in invasive infection among persons 65 years or older.

The authors conclude that the pneumococcal conjugate vaccine was already effective within the first year of widespread use, reducing rates of invasive disease. This protection extends beyond the intended target population of children younger than two years.