WHEN THE VACCINE CAUSES THE POLIO

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After weighing the risks and benefits, the CDC panel decided to split the difference. Their recommendation, which is slated to become official policy in 1996, is to inoculate infants twice with the killed-virus vaccine at two and four months, then twice more with the live-virus vaccine before the age of six years. Infants, whose immune systems are not yet very strong, do not get exposed to the slightly more dangerous preparation. Older children, who have developed tougher constitutions, will get the benefits of full protection. Experts expect that the change could prevent most vaccine-associated cases of polio.

It will be a tough sell. As Dr. Ram Yogev of Children's Memorial Hospital in Chicago points out, the Sabin vaccine worked so well that health workers may resist the change. Says Dr. Yogev, who favors the change himself: "Physicians respect Salk. But we love Sabin because we saw the epidemic. We were a part of it, and suddenly it disappeared."

Inconvenience and expense are also factors. The Sabin vaccine comes in a sweet-tasting liquid, but the Salk vaccine can only be injected. Parents and youngsters will not welcome another shot in the already packed vaccination schedule. The injections cost more ($4.99 a dose in the public market vs. $2.27 for the live virus) and may mean another trip to the doctor. Some are worried that the immunization rate, particularly in inner cities, will drop.

One person who has no doubt that the CDC made the right choice is 10-year-old Ryan. Although plucky enough to play Little League baseball with a pinch runner, he has his down moments. "I hate this polio," he says. "Even if it was for just one day, I wish I could run." That may never happen, but if all goes as expected, fewer children will find themselves in Ryan's shoes.

--Reported by Scott Norvell/Atlanta and Alice Park/New York