Population-Based Surveillance for Childhood Invasive Pneumococcal Disease in the Era of Conjugate Vaccine. Hsu K, Pelton S, Karumuri S, Heisey-Grove D, and Klein J. Pediatric Infectious Disease Journal, 2005;24(1):17-23.
Explanatory note: Serious bacterial infections, such as pneumonia requiring hospitalization and bacterial meningitis used to be common illnesses with potentially life threatening and damaging consequences in young infants and children. Many of these diseases have become uncommon since the Haemophilus influenzae type b (Hib) conjugate vaccine was introduced in 1988. Much of the remaining diseases of these types are caused by Streptococcus pneumoniae, a similar but unrelated bacterium. Unlike Hib, for which there was only one type, there are more than 90 types (or serotypes) of S. pneumoniae.
A 7-valent pneumococcal conjugate vaccine (PCV7), which contains the 7 most common pneumococcal serotypes causing invasive (serious) infections in children, was licensed in February 2000 in the United States for routine administration to children beginning at 2 months of age. During much of the first 3 years after licensure, this vaccine was in short supply.
What has been the impact of the recommendation for universal PCV7 vaccination on childhood invasive pneumococcal disease (IPD) in Massachusetts?
Researchers identified the number of new cases of IPD occurring between October 2001 and September 2003 in children in Massachusetts. The cases were identified through laboratory reports of positive cultures of S. pneumoniae to the Massachusetts Department of Public Health (MDPH) via a combination of active (phone calls to labs) and passive surveillance.
Epidemiologists from the MDPH then interviewed the case’s primary care provider to determine the age, gender, race, vaccination status, clinical presentation and underlying medical conditions.
Parents or guardians were also interviewed to confirm race and identify day-care attendance and household information such as occupancy number. This information was gathered to examine predisposing factors for developing IPD.
The incidence of IPD was compared to 1990-1991, a year during which similar surveillance was conducted before PCV7 licensure.
This study identified 191 cases of IPD during the 2-year study period, 138 (72%) of which occurred in children younger than 5 years of age. The annual incidence rate for invasive disease was 17.4 per 100,000 children younger than 5 years of age during the study period; before PCV7 was licensed (i.e. 1990-1991) the incidence rate was 56.9 per 100,000 per year, a 69% decline in the rate of IPD.
There was also a small increase in the incidence of nonvaccine serogroups causing IPD. The study also found that IPD was more common in blacks and Hispanics than in whites, in children younger than 1 year of age, and in children with underlying diseases such as sickle-cell disease or HIV infection.
Only a small proportion of observed disease was attributable to vaccine failure. Very few cases were attributed to vaccine shortage.
Compared with the prior studies, Massachusetts has had a decline of IPD among children younger than 5 years of age. Blacks and Hispanics continue to suffer increased rates of IPD, in contrast to other studies.
A number of recent studies have also demonstrated that vaccination of children with PCV7 has reduced IPD. A concern arising from this study also observed in another study was an increase in the number of cases due to nonvaccine serotypes.
While the results of an increasing number of studies suggest a dramatic reduction in cases of IPD since the introduction of the PCV7 vaccine, it is important to recognize that the passive reporting of cases both in this study and the one a decade earlier limit the interpretation of these data.