GAITHERSBURG, Md. (AP) - Early research in older adults found an experimental vaccine prevented nearly two-thirds of serious cases of a common, seasonal respiratory virus that annually kills thousands of vulnerable people - babies and senior citizens.

GAITHERSBURG, Md. (AP) Early research in older adults found an experimental vaccine prevented nearly two-thirds of serious cases of a common, seasonal respiratory virus that annually kills thousands of vulnerable people babies and senior citizens.

If further testing by vaccine developer Novavax Inc. goes well, in a few years the biotech company's genetically engineered shot could become the first vaccine approved against respiratory syncytial virus, or RSV.

That would be a breakthrough, as drugmakers have unsuccessfully tried to create a vaccine against RSV for the last half-century. Novavax, based in Gaithersburg, Maryland, says it's figured out how to make the immune system detect and block the tough-to-spot virus by synthetically building one of its proteins.

There's no treatment for RSV other than supplemental oxygen and other intensive medical care.