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Fear of ReplacementWhat if a vaccine kills off one strain of a disease—but makes room for another?

By Arthur AllenPosted Thursday, June 21, 2007, at 12:00 PM ET

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Even here, the threat may not be as great as the JAMA study suggests. It's true that since the Prevnar vaccine began to be used, invasive disease caused by the virulent pneumoccocus strain 19A has tripled in the United States, from about 3 per 100,000 to 9 per 100,000. But those numbers are small when compared with the overall decrease in invasive disease caused by all pneumococci—from 100 per 100,000 to 25 per 100,000 over the same period.

The question is whether 19A or other strains not covered by existing vaccines will push their way further into the niche left by the strains of the bacteria being eliminated. The verdict is out on that. Replacement strains of pneumococcus aren't striking as quickly elsewhere in the country as they are in Alaska. For example, Apache children in Arizona began getting the Prevnar shot in 1997, but there has been no replacement effect among them. And in Israel and South Korea, which haven't introduced Prevnar, 19A infections have also been growing. This indicates that 19A may be on a cyclical upswing for reasons that have nothing to do with the vaccine.

Meanwhile, the pharmaceutical industry seems poised to fight 19A to preserve the successes of Prevnar, as well as the promise it holds for the Third World. The vaccine has been a blockbuster for Wyeth by virtue of its many health benefits. With this track record in mind, do-gooders are planning a major new initiative that would allow the world's poorest countries to offer Prevnar with a small "co-pay," with the balance to be picked up by a coalition of wealthy countries and the Gates Foundation (the Bush administration has declined to back the program, known as the advanced market commitment). Gambia and Kenya are expected to begin using the vaccines next year, following a successful trial in Gambia: For every 1,000 babies who got Prevnar during the trial, seven survived who would have otherwise died.

Scientists working on this global campaign caution against reading too much into the Alaska data. They point out that even if replacement disease continues to grow, the drug companies may have an answer. Wyeth, for example, isn't taking chances on 19A. The company is developing a 13-strain vaccine that contains the virulent bug and others, and is scheduled to be ready by 2010. Competitor GlaxoSmithKline is also working on a new pneumococcal vaccine. If we needed a reminder, the JAMA paper shows once again that the fight against infectious disease isn't simple. Germs have a way of keeping us on our toes.