The infant pneumococcal vaccine introduced 10 years ago has cut rates of pneumonia, meningitis and other infections among Navajos in the U.S. - but their risks remain higher than average, a new study finds.

The pneumococcal conjugate vaccine, commonly known as PVC7, was licensed in 2000 for protecting young children against several strains of the Streptococcus pneumoniae bacterium. The bug causes a range of infections, including so-called invasive pneumococcal disease (IPD) - pneumonia, meningitis and bacteremia (a blood infection).

Before the vaccine was introduced, Alaskan Natives, Navajos and White Mountain Apaches were known to have rates of IPD up to 20-times greater than that of the general U.S. population.

In the new study, researchers found that cases of IPD caused by the bacterial subtypes covered by the PVC7 vaccine have been “virtually eliminated” from the Navajo Nation since the vaccine’s introduction.

Dr. Katherine L. O’Brien and colleagues at Johns Hopkins University in Baltimore found that between 2004 and 2006 - the latest year for which they had data - there were no cases of vaccine-type IPD among children younger than 5.

In contrast, between 1998 and 2000, there were 214 cases per 100,000 children between the ages of 1 and 2, and 161 cases per 100,000 children younger than 1 year.

Among adults age 65 or older - the other age group at particular risk for IPD - rates of vaccine-subtype infections fell 81 percent after the vaccine was introduced. Between 2004 and 2006, there were four cases of IPD per 100,000 adults in that age group.

The decrease among older adults is in line with research showing that vaccinating and preventing pneumococcal disease in children helps protect older adults as well.

Despite that success, however, the overall IPD rate remains four times higher among Navajos compared with the general U.S. population, O’Brien’s team reports in the journal Clinical Infectious Diseases.

Among children younger than 5, Navajos still have IPD rates more than four-fold higher than those in the overall U.S. population - with all cases caused by non-vaccine strains.

Similarly, adults age 65 and up showed no changes in their rate of IPD from non-vaccine strains between 1995 and 2006. Between 2004 and 2006, there were 159 cases per 100,000 adults in that age group.

The findings highlight a need for more preventive measures, according to O’Brien’s team.

Studies have pointed to a number of reasons for the elevated IPD risk among Navajos and other Native groups - including, among adults, relatively high rates of heart disease, alcoholism and diabetes, which can make people more vulnerable to pneumococcal infection; and, among children, higher rates of influenza and other viral respiratory infections.

More effort needs to go toward control those risk factors, O’Brien and her colleagues write.

Earlier this year, the U.S. Food and Drug Administration approved a “PCV13” vaccine, which covers six additional S. pneumoniae subtypes, for infants and young children.

But, O’Brien’s team says, even if that vaccine turns out to be 100-percent effective against all 13 strains, IPD rates among Navajo children younger than 5 will likely stand at about 20 cases per 100,000.

The study was partially funded by Wyeth Pharmaceuticals, which manufactures the PCV7 and PCV13 vaccines. O’Brien and a co-author on the study have received grants from the company.

SOURCE: http://www.journals.uchicago.edu/doi/abs/10.1086/651680 Clinical Infectious Diseases, May 1, 2010.