Malaria is a very serious disease that kills more children under the age of five than any other disease. People get malaria when they are bitten by tiny insects called mosquitoes. The mosquitoes carry parasites（寄生蟲）which enter a person's blood and cause malaria.

Carter Dibbs is an American doctor who works on the Malaria Vaccine Development Program for the United States Agency for International Development. Doctor Dibbs says the parasite that causes malaria is much more complex than other organisms, such as the virus that causes polio. He says the malaria parasite uses many tricks so that it is more difficult to make a vaccine（疫苗）that is safe and will prevent the disease.

Malaria vaccines are now being tested on adults in Burkina Faso and Mali. Vaccines are being tested on children in Mozambique and Mali.

Many organizations are involved in the testing. They include U.S.A.I.D, the American military, American health organizations, and European governments.

To make sure that a vaccine will really prevent malaria, it must be tested on many people in many different places. Doctor Dibbs says the people who join the vaccine tests are as important to the goal of finding the right medicine as the scientists.

People are told about the tests during public meetings with community leaders. Doctor Dibbs says people should ask questions about good or bad things that could happen to their bodies if they take the medicine that is being tested. Adults or parents of children must agree to the vaccine test.

Adults receive a small amount of the vaccine medicine. The children receive either the malaria vaccine or a different medicine that protects them against a different disease.

Then health care workers observe the people to see if they show any signs of malaria. The results of the tests must be compared to people who have not received the vaccine.

The vaccine is successful if fifty percent of the people who receive it do not show any signs of malaria for one year.

Then the United States government will be asked to approve the vaccine. However, it could still take another five years before a licensed vaccine is ready to give to all the children in Africa and around the world.

This VOA Special English Development Report was written by Karen Leggett. This is Robert Cohen.