Decreased Invasive Pneumococcal Disease in Adults after PCV 7

Abstract

Source: Flannery B, Heffernan RT, Harrison LH, et al. Changes in invasive pneumococcal disease among HIV-infected adults living in the era of childhood pneumococcal immunization. Ann Intern Med. 2006;144:1–10.This observational study employing historic controls examined rates of invasive pneumococcal disease in HIV- and non-HIV-infected adults in 7 metropolitan areas in the US before and after the introduction of conjugate pneumococcal immunization (PCV 7) in children. The surveillance was conducted through the Emerging Infections Program network of the Centers for Disease Control and Prevention for cases diagnosed between January 1, 1998 and December 31, 2003. The 7 sites included San Francisco County, Calif; the state of Connecticut; metropolitan Atlanta, Ga; metropolitan Baltimore, Md; metropolitan Minneapolis-St. Paul, Minn; metropolitan Portland, Ore; and a collection of Tennessee counties. Cases were included if pneumococcus was isolated from any normally sterile site. The investigators compared rates before and after routine PCV 7 vaccination in infants in 2000.A total of 8582 cases of invasive pneumococcal disease occurred in adults aged 18 to 64 years, and 2013 (24%) of these were among patients with HIV infection. The authors found a decrease in incidence in non-HIV-infected adults from 13 (in 1998–1999) to 9 (in 2003) cases per 100,000 (P<.001), driven by declines in the serotypes present in PCV 7. Because the authors could not determine the total number of HIV-infected individuals living in the surveillance areas, they could not provide exact incidence rates for this population. However, they did determine the ratios of invasive pneumococcal disease in HIV-infected adults to the number of adults living with AIDS in the area as a proxy measurement. By this yardstick, ratios decreased from 1127 to 919 cases of invasive pneumococcal disease per 100,000 AIDS population over the study period, a 19% reduction (P=.002). Among HIV-infected adults, there was a 62% decrease (P<.001) in the serotypes present in conjugate vaccine, but a 44% increase in all other serotypes (P<.001), including those in the polysaccharide vaccine.Dr. Robbins has disclosed no financial relationship relevant to this commentary. This commentary does not contain a discussion of a commercial product/device. This commentary does not contain a discussion of an unapproved/investigative use of a commercial product/device.For pediatricians to see the benefits of their preventive health efforts is heartening, and indirect benefits in other population groups is a bonus. Since the introduction of PCV 7 for infants in the US, the incidence of invasive pneumococcal disease in adults due to vaccine serotypes has decreased. What is a bit surprising is that although HIV-infected adults had an overall decline in pneumococcal disease, there was a significant increase in disease caused by non-vaccine strains of pneumococcus, and that the “serotype replacement phenomenon” was seen only among the HIV-infected adults. So, it would seem that a marked benefit of childhood PCV 7 is seen in non-HIV-infected adults, but to a lesser extent among HIV-infected adults. The serotype replacement phenomenon has important implications for developing countries with higher HIV infection rates.The authors acknowledge that their method of determining the ratio of invasive pneumococcal disease cases to the number of adults living with AIDS is only a proxy of the true incidence rates, which they could not determine. Also, they lacked information about degree of immunosuppression and use of antiretroviral therapy in these patients, factors that would be expected to have a large bearing on susceptibility to pneumococcal disease. While the introduction of infant PCV 7 would seem to be the most likely explanation for this disease decline, these data can show only an association and do not prove cause and effect.