Pneumococcal Strains Not Covered by Vaccine on the Rise

TUESDAY, April 24 (HealthDay News) -- While the pneumococcal vaccine for children is highly effective, strains of the bacteria not covered by the vaccine are emerging as potential threats in certain populations.

A new U.S. government investigation has found that in Alaskan Native children who are already protected against seven strains of pneumococcal disease due to vaccination, the rate of serious infection by other strains is increasing by as much as 140 percent.

"The vaccine has been very effective and has done exactly what we hoped it would do. It's decreased the incidence of invasive pneumococcal disease (covered by the vaccine strains) by 95 percent in Alaskan Native children," said the study's lead author, Dr. Rosalyn Singelton, a visiting researcher for the U.S. Centers for Disease Control and Prevention in Anchorage, Alaska. "But, we've recently seen a significant increase in emerging non-vaccine serotypes."

The bacterium Streptococcus pneumoniae causes a variety of pneumococcal diseases, according to the CDC. Some are relatively mild, such as ear infections, while others are potentially life-threatening, such as pneumonia, meningitis and blood infections.

In 2000, the PCV7 pneumococcal conjugate vaccine first became available for infants and children. The vaccine includes the seven strains or serotypes of the bacteria that commonly cause pneumococcal disease in the United States.

Alaskan Natives have traditionally had higher rates of pneumococcal disease, according to the study. Before the introduction of the PCV7 vaccine, Alaskan Native children had three times the rate of invasive pneumococcal disease compared to the overall U.S. population. Possible reasons for this, according to Singleton, were overcrowding in small households, spending large amounts of time indoors and a lack of running water in many communities.

The new study, published in the April 25 issue of the Journal of the American Medical Association, included surveillance data from the beginning of 1995 through 2006.

The researchers found that within three years of the introduction of the vaccine, the overall rates of invasive pneumococcal disease in Alaskan Native children under age 2 was down by 67 percent.

However, when the researchers compared the two-year periods of 2001-2003 to 2004-2006, they saw an 82 percent increase in the rate of overall invasive pneumococcal disease in Alaskan Native children under 2. For strains not covered by the vaccine, the rate jumped by 140 percent compared to the pre-vaccine period.

One strain in particular, serotype 19A, was responsible for almost one-third of the non-vaccine covered disease, according to the study.

"This is a warning sign that this may occur in other populations," said Singleton, who pointed out that researchers have already been anticipating this shift and are working on second-generation pneumococcal vaccines.

Dr. Katherine Poehling, a pediatrician at Brenner Children's Hospital at Wake Forest University School of Medicine in Winston-Salem, N.C., said, "The serotype replacement is occurring to a greater extent in this (Alaskan Native) population, but it will happen in others."

Poehling, who wrote an accompanying editorial in the same issue of the journal, said, "This study is helping us to make sure that we maintain the magnificent gains we've seen over the last seven years."

Along with receiving the pneumococcal vaccine, Singleton said that other potential ways to reduce the incidence of disease are good hand-washing, breast-feeding your baby if you can, and delaying putting children into day care if possible.

More information

Read more about pneumococcal infections at the U.S. National Foundation for Infectious Diseases.

SOURCES: Rosalyn Singleton, M.D., M.P.H., visiting researcher, U.S. Centers for Disease Control and Prevention, and Alaska Natives Tribal Health Consortium, Anchorage; Katherine Poehling, M.D., M.P.H., pediatrician, Brenner Children's Hospital, Wake Forest University School of Medicine, Winston-Salem, N.C.; April 25, 2007, Journal of the American Medical Association