Chicken pox, long considered an inevitable consequence of childhood, could soon be reclassified as a preventable illness in children, thanks to a new vaccine currently being tested.

The new vaccine is being tested in healthy children and in youngsters with lymphocytic leukemia, researchers reported at the American Academy of Pediatrics' annual spring meeting held last week in Orlando, Fla. About 7 percent of the young leukemia patients who contract chicken pox die, said Dr. Philip Brunell, chief of pediatric infectious diseases at the University of Texas Health Science Center in San Antonio.

To date, the vaccine has prevented chicken pox, or varicella, in more than 95 percent of the several thousand youngsters who have received it, according to Merck Sharp and Dohme, the drug company that is developing the vaccine for the U.S. market. Similar vaccines are already in use in Japan and Europe.

If tests continue to be successful -- and if the Food and Drug Administration approves the new vaccine -- parents and children could begin seeing it on the market in the next year to 18 months. The vaccine will be given to children during the second year of life, and, based on overseas experience, will cost about $15 to $20.