News

While a new vaccine has all but eradicated common causes of pneumonia, meningitis and ear infections in children, new strains of bacteria not covered by the vaccine have emerged, researchers are warning.

Two new studies from Alaska and from Spain suggest that serotypes or strains of pneumococcal bacteria not covered in the vaccine - sold as Prevnar - are stepping into the void left by those the does protect against.

"I think we knew there was that potential for that to occur, but there was no way to predict if it would occur, or to what extent," Rosalyn Singleton, lead author of the first study, said from Anchorage.

Dr. Singleton's study was on native children in Alaska, a group particularly prone to infection with pneumococcal bacteria, which can cause illnesses ranging from ear and sinus infections to serious bloodstream infections, meningitis and pneumonia. But she believes what she and her co-authors are seeing in Alaska has the potential to spread elsewhere.

"This is a phenomenon which may increase and be seen in other populations," said Dr. Singleton, a pediatrician and immunization consultant with the Alaska Native Tribal Health Consortium in Anchorage and a visiting researcher with the U.S. Centers for Disease Control and Prevention.

The Spanish study, by researchers at the University of Navarra, also showed an upswing of cases caused by non-vaccine strains after immunization with Prevnar began.

It had been known that this phenomenon, called replacement disease, can occur with the widespread adoption of a new vaccine that targets only some strains of a pathogen. In fact, public health authorities will be looking to see if the new human papillomavirus vaccines produce this effect.

But replacement disease is not inevitable. So public health officials always hope it won't rear its head and undermine the impact of new and often expensive vaccines.

These new studies - Dr. Singleton's appears in today's edition of the Journal of the American Medical Association, the Spanish study is slated for the June issue of Clinical Infectious Diseases - suggest that within a couple of years of Prevnar hitting the market there was a renewed surge in disease caused by pneumococcal serotypes not included in the vaccine.

(Prevnar targets seven of roughly 90 serotypes. While it's not believed that all of those serotypes can cause significant disease, some clearly can. And Prevnar's maker, Wyeth Pharmaceuticals, is currently testing a second-generation pneumococcal vaccine that would protect against 13 serotypes.)

Prevnar is provided free of charge by all provinces and territories in Canada. But most jurisdictions only started offering the vaccine in 2005, so an upswing of disease caused by non-vaccine strains wouldn't be expected for a while in Canada, said Canadian vaccine expert Dr. David Scheifele.

Katherine Poehling, a vaccine expert at Wake Forest University Baptist Medical Center in Winston-Salem, N.C., said the emergence of replacement disease now is actually a "good news" story.

"The vaccine is highly effective and it remains effective," Dr. Poehling said. "And so it gives us the opportunity to intervene while [people] maintain benefits. Because if we weren't doing surveillance, we'd have no idea. And you don't want to wait until you're back to where you were before you recognize a problem."

But Allison McGeer, an infectious disease expert at Toronto's Mount Sinai Hospital, said the need for a new vaccine that protects broadly against the pneumococcal family could drive the price beyond the capacity of publicly funded programs.