The U.S. drug company Chiron is recalling a vaccine for measles, mumps and rubella that it supplies to developing countries and Italy. The company says the vaccine has a higher rate of adverse side effects than similar drugs.

Chiron distributed about five million doses of its Morupar vaccine in 2005, most of it to the developing world through the United Nations Children's Fund, or UNICEF, and the Pan American Health Organization. Recipient countries included Syria, Jordan, Argentina and Egypt. About 450,000 doses were supplied to Italy.

A spokeswoman for the California company said adverse responses were rare, but occurred in higher numbers than with similar vaccines, and included fever, allergic reactions, and the swelling of glands. She says no deaths have been reported. She says Chiron is withdrawing the drug from the market as a precaution, as it awaits results of a risk-benefit study by the World Health Organization.

The recall does not affect Chiron's other vaccines. And other drugs that immunize against measles, mumps and rubella remain on the market. Measles vaccines are considered highly effective, and have been available for 40 years. The first combined measles-mumps-rubella (MMR) vaccine was introduced in 1971.

Measles is a leading cause of death among children in developing countries, and world health officials say those in sub-Saharan Africa are especially at risk. Last week, the World Health Organization announced a dramatic reduction in measles deaths in sub-Saharan Africa after a six-year immunization program. The program targeted 47 countries around the world that account for most fatalities from measles. Health officials said progress in South Asia has been slower.

Chiron faced another problem in 2004, when it failed to deliver nearly 50 million doses of influenza vaccine to the U.S. market after British regulators found contamination at a Chiron plant in England.