The incidence of pneumonia among older adults has decreased substantially, linked to the introduction of a pneumonia vaccine for children in 2000, according to a study in the Oct. 26, 2005 issue of JAMA.
The pneumococcal conjugate vaccine (PCV-7) was licensed for use in infants and young children in March 2000, according to background information in the article. Use of PCV-7 in children can affect pneumonia transmission in the community. Pneumonia causes substantial illness and death among older adults. Consistent with the ability of PCV-7 to interrupt transmission, declines in invasive pneumococcal disease incidence among older adults were observed in 2001, the year after PCV-7 introduction.
Catherine A. Lexau, PhD, MPH, of the Minnesota Department of Health in St. Paul, Minn., and colleagues conducted a study to determine whether the observed early decline among adults aged 50 years and older has continued over the four years since pneumococcal conjugate vaccine licensure, whether disease characteristics have changed, and whether the spectrum of patients acquiring invasive pneumococcal disease has changed. The study included population-based surveillance data of invasive pneumococcal disease in eight U.S. geographic areas (total population, 18,813,000), 1998-2003.
The researchers found that the incidence of invasive pneumococcal disease among adults aged 50 years or older declined 28 percent, from 40.8 cases/100,000 in 1998-1999 to 29.4 in 2002-2003. During 2002 and 2003, the overall rate of invasive disease among persons aged 65 years or older (41.7 cases/100,000) was lower than the Healthy People 2010 goal of 42 cases/100,000. Among adults aged 50 years or older, incidence of disease caused by the seven conjugate vaccine serotypes declined 55 percent from 22.4 to 10.2 cases/100,000.
In contrast, disease caused by any of the 16 serotypes only in polysaccharide vaccine did not change, and disease caused by serotypes not in either vaccine increased somewhat, from 6.0 to 6.8 cases/100,000. Between 1998-1999 and 2002-2003, the proportion of case-patients with human immunodeficiency virus infection increased from 1.7 percent (47/2,737) to 5.6 percent (124/2,231), and those with any co-existing illness that is an indication for pneumococcal polysaccharide vaccination increased from 62.3 percent (1,842/2,955) to 72.0 percent (1,721/2,390).
The researchers estimate that 12,500 fewer cases and 1,100 fewer deaths occurred among older Americans in 2002 and 2003, compared with the numbers of cases and deaths occurring before the vaccine was available.
Several factors support the hypothesis that the declines in invasive disease reported here likely occurred because of decreased community transmission of vaccine-type pneumococci from young children, many of whom have received PCV-7. Studies of pneumococcal carriage indicate that conjugate vaccines reduce carriage of vaccine-type pneumococci in vaccinated children. Likewise, unvaccinated children in close contact with vaccinated children or living in communities in which the vaccine is being used also have experienced reductions in pneumococcal carriage and disease caused by PCV-7 serotypes. In this analysis, the overall decline in invasive disease incidence was mainly due to a decrease in disease caused by PCV-7 serotypes, suggesting a specific conjugate vaccine effect. In addition, the timing of the changes among older adults coincided with uptake of vaccine in children; incidence first declined in 2001, following initial use of PCV-7 among young children in the last half of 2000, and then dropped further in 2002-2003 as vaccine coverage in children increased, the authors write.
We have documented a consistent decrease in incidence of invasive pneumococcal disease in an age group at high risk for serious disease and death from these illnesses. Policy makers elsewhere who are considering whether to incorporate PCV-7 into their routine infant immunization programs and who are weighing its cost-effectiveness should consider the benefits seen in older adults. However, it is unknown whether this herd effect will be similar in all settings and population subsets. The size of the effect may differ in populations with different serotype distributions or with a higher or lower prevalence of chronic conditions among older adults. We look forward to results from other populations to see if similar effects will occur. In the U.S. population, use of PCV-7 for children has been an effective means of preventing disease in older adults, the researchers conclude.
Reference: JAMA.2005; 294:2043-2051
Source: American Medical Association