German measles (search), which expectant mothers once feared contracting because of prenatal complications, is no longer a health threat in the United States, federal authorities say.

Medical experts welcomed the word Friday from the Centers for Disease Control and Prevention, but said it doesn't mean there should be a letup in childhood vaccinations for rubella (search), the formal name for German measles.

While U.S. residents no longer develop German measles and pass it on to others in this country, the disease can still be imported through visitors from foreign countries.

"It is not the case we can stop immunizing. We must continue to keep immunizing," said Dr. Greg Poland, professor of medicine and infectious diseases at the Mayo Clinic in Rochester, Minn. "Continued cases come in, particularly from the southern border. It's still an active disease in Mexico."

Poland said he saw a case of rubella just a few years ago in a pregnant migrant laborer living near Rochester.

Rubella typically causes a mild rash and, unlike measles, is not considered to be a serious illness for most people. However, the disease is much more hazardous for pregnant women.

When expectant mothers in their first trimester contract rubella, the risk of infection to the fetus can be 90 percent, often resulting in a miscarriage, stillbirth or severe birth defects.

Congenital rubella syndrome in infants is still a severe problem in other parts of the world, with more than 100,000 cases reported annually, according to a 2002 survey published by the CDC.

Only 11 cases of congenital rubella syndrome were reported in the United States in 2000 and 2001, the survey noted.

CDC officials declined to publicly discuss the rubella situation in advance of an official announcement Monday by the agency's director, Dr. Julie Gerberding.

A vaccine for rubella was invented in 1969 by Dr. Maurice Hilleman, director of the Merck Institute for Vaccinology. In 1969, nearly 60,000 cases of rubella were reported in the United States. By 2000, only 176 cases were reported.

Dr. Ronald Davis, a trustee at the American Medical Association, said the eradication of rubella among U.S. citizens gives the nation all the evidence it needs that it should do a better job at vaccinating the population from other diseases, such as influenza and hepatitis B.

He said he remains worried that some people will take the news about rubella the wrong way.

"What public health officials worry about is that when disease levels go down, public attention wanes and immunization rates may decline. Then the disease occurrence could rebound," Davis said.

Children generally get their first vaccination dose for rubella at about 12 months of age. They are supposed to get a second dosage when they become of school age, Poland said.