The seven-valent pneumococcal conjugate vaccine (PCV7), was added to the Recommended Childhood Immunization Schedule in 2001, leading to a marked decline in the incidence of invasive pneumococcal disease. Before the vaccine was introduced, blacks in the United States were far more likely to have pneumococcal disease than whites. Did the vaccination have an impact on this racial disparity?
To answer that question, investigators analyzed data from the 2001 and 2002 Active Bacterial Core Surveillance/Emerging Infections Program Network, a surveillance system in seven states. Between 1998 and 2002, the annual rate of invasive pneumococcal disease declined: from 19.0 to 12.1 cases for every 100,000 white persons and from 54.9 to 26.5 among blacks. Compared with the prevaccine period, the incidence of invasive pneumococcal disease was lower for whites and blacks in every age category in 2001 and 2002, with the greatest reduction seen among children younger than 2 years. In that age group, the ratio of black-white incidence was significantly lower than in the earlier period and, in 2002, was nearing equality. Among children 2 to 4 years old, the black-white ratio also was lower in 2002 than in the prevaccine period, although the difference was statistically insignificant.
Overall, the ratio of black-white incidence of invasive pneumococcal disease among children fell from 2.9 in 1998 to 1999 to 2.2 in 2002. Blacks still experienced a significantly higher rate of disease than whites in almost every age category, but the difference between the rate for blacks and the rate for whites fell 60% (Flannery B et al: JAMA 2004;291:2197).
Commentary: The first two years of PCV7 saw a decline in the incidence of disease in both blacks and whites, but that decline was significantly greater in blacks. Reasons for the disparity in disease and in improvement are not entirely clear. And, at least in children younger than 2 years, the explanation does not appear to be a difference in the immunization rate. The benefit of the vaccine extended beyond the age at which children were vaccinatedpresumably, as a result of protective herd immunity.
This is good news, even without a full explanation.