【听力原文】
The United States government has begun the first clinical testing of an experimental vaccine designed to guard against Zika virus.
The National Institute of Allergy and Infectious Diseases made the announcement earlier this week.
The experimental vaccine has already been tested in animals.
Anthony Fauci, the institute's director, said on Wednesday that investigators should know soon whether the vaccine is safe for use in human beings. He said the first human tests involve 40 human volunteers in the U.S.
"If we get a good immune response and there are no safety red flags by the end of December 2016, we should know if it's okay to move on to phase II." He said the second phase could begin early next year.
Those trials will be larger studies, involving more volunteers. They would be performed in countries where Zika has spread. There, researchers would look not only at the safety of the experimental vaccine, but its effectiveness in fighting infection.
Infected mosquitoes can pass the virus to people. It can also be passed through sexual contact.
Zika usually causes minor problems in healthy people. But there is a real danger if an infected insect bites a pregnant woman. The infection could spread to the fetus she is carrying.
If infected with the virus, women can give birth to babies with a severe condition known as microcephaly. The heads and brains of those babies are unusually small. Microcephaly can cause many mental and physical problems and even death.
At first, the vaccine's main target will be women of the age when many women give birth. Researchers would also be looking to prevent the disease in the general adult population.
New technique
The vaccine was developed with a relatively new technology. It was scientifically engineered to contain a small piece of DNA from the virus. DNA is short for deoxyribonucleic acid, which contains the biological commands for Zika. The piece is so small that it is not infectious. But it is big enough to produce a reaction from the body's natural defenses for fighting disease.
Fauci said the DNA method makes it easy to provide the vaccine quickly. "We cannot afford to delay the development of a safe and effective vaccine to prevent Zika virus infection," he added.
Zika infections have been reported in 50 countries and territories. Most cases are in Central and South America and the Caribbean. This week, U.S. officials announced that a number of people in the state of Florida have been infected. They said all the infections resulted from infected mosquitoes.
I'm Anne Ball.
Jessica Berman wrote this story for VOANews. Jim Dresbach adapted it for Learning English. George Grow was the editor
