Pneumococcal Disease Rebounding in Alaskan Native Children

ANCHORAGE, April 24 -- After responding well to the heptavalent childhood pneumococcal vaccine for three years, Native Alaskan children are falling ill from strains of Streptococcus pneumoniae not covered by the vaccine, according to the CDC.

Compared with the pre-vaccine period, the rate of overall invasive pneumococcal disease fell 67% in native Alaskan children younger than two in 2001 through 2003, the first three years after the vaccine was introduced, said Rosalyn Singleton, M.D., of the CDC's Arctic Investigations Program here.

But in the following three years -- 2004 through 2006 -- the rates increased again, by 82% compared with the previous three years, Dr. Singleton and colleagues reported in the April 25 issue of the Journal of the American Medical Association.

Since 2004, Dr. Singleton and colleagues said, the rate of disease caused by non-vaccine strains of S. pneumoniae has increased by 140% compared with the pre-vaccine period.

In contrast, there has been no rise in non-vaccine strains infections among non-native children.

The findings show that the vaccine was highly successful, the researchers said, but reinforce concerns that non-vaccine serotypes of the bacteria would replace those that had previously caused the majority of disease.

Indeed, the research indicates that invasive pneumococcal disease is "a moving target," according to Timothy Peters, M.D., and Katherine Poehling, M.D., both of Wake Forest of Winston-Salem, N.C., in an accompanying editorial.

The vaccine itself has been a "towering success," they wrote, but victory cannot yet be declared, because a so-called serotype replacement has now been shown to be a consequence of the vaccine.

Continued surveillance and vaccine design that adapts to changing conditions are needed to "defend the idea that humankind will ultimately be free of pneumococcal disease," they said.

In Alaska, the pneumococcal vaccine program was rolled out quickly after it was approved in 2000, and coverage was - and has remained - high, reaching 96% among native children 19 to 35 months with electronic data records.

Analysis of pneumococcal disease among native children younger than two, using CDC records, showed:

• The rate of invasive pneumococcal disease was 403.2 per 100,000 in 1995 through 2000.
• It declined to 134.3 per 100,000 per year in 2001 through 2003, a reduction that was statistically significant at P<0.001.
• Compared with 2001 through 2003, the rate rose again in 2004 through 2006 to 244.6 per 100,000, which was significant at P=0.02.
• The invasive pneumococcal disease rate caused by non-vaccine serotypes went from 95.1 per 100,000 in 1995-2000 to 228.6 in 2004 through 2006, an increase that was significant at P=0.001.
• At the same time, disease caused by the seven vaccine serotypes fell by 96%.

Native Alaskan children have historically had higher rates of invasive pneumococcal disease - about 450 per 100,000 yearly -- than their non-native counterparts, Dr. Singleton said in an interview.

The reasons, she said, include over-crowded and sometimes substandard housing, combined with a lack of running water and flush toilets, that provide an opportunity for bacteria to spread.

Alsol, she said, because of the Arctic conditions, people spend a great deal of time indoors and exposed to bacteria.

The crowding might also help explain why the non-vaccine strains emerged so quickly, Dr. Singleton said.

Alaskan natives have a high rate of carriage of many strains of S. pneumoniae, she said, and the rapid introduction of the vaccine made it "possible for one (non-vaccine) type to emerge and spread quickly."

Characteristics of the different strains probably also play a role in which of them emerge as disease pathogens, she said.

A rise in non-vaccine disease has not been seen in other child populations, including some that might be thought similar to Alaskan natives -- Navajo or Australian aboriginal children.

In the case of the Navajo, the researchers said, the introduction of the vaccine was slower, while in Australia, the initial shots of the heptavalent vaccine were followed with a 23-valent booster shot.