Health experts have a new warning about Zika virus. They say the virus will keep spreading before the Zika epidemic finally ends.

The experts say a new model shows a very large number of people could become infected before then. The model is a project of researchers from England, Sweden and the United States.

They estimate the Zika virus could infect over 93 million people in South America, North America and the Caribbean. The model projects 1.6 million young women could be infected.

Experts say a woman who is infected during the early months of her pregnancy is at risk of giving birth to a baby with microcephaly. A baby born with microcephaly has a small head and brain.

The condition causes mental and physical disability, seizures and sometimes death. But experts say not every pregnant woman infected with Zika will give birth to a child with severe birth defects.

The Associated Press says the Zika virus is spreading quickly in South America and the Caribbean. Infected mosquitoes can pass the infection to humans.

Over 1,400 cases of the Zika virus have been reported in the U.S., according to the Centers for Disease Control.

The Zika study was published in the journal Nature Microbiology. It is the most detailed estimate to date about the spread of the virus.

In developing their study, researchers used information from past epidemics of two other viruses: dengue and Chikungunya.

Dengue is in the same virus family as Zika. Chikungunya is also spread by mosquitoes. The viruses can cause headaches, muscle pain and higher than normal body temperature. But 80 percent of people who contract Zika have no symptoms.

Researchers also examined data on blood tests from people who have been infected with Zika. That gave them information to predict the rate of transmission at the local level.

Unique model

The model took into consideration how an event called herd immunity can change the number of infections. Herd immunity happens when a disease or virus can no longer spread because so many people are infected. When that happens, others are protected against the disease.

"So really there's going to be a large proportion of the population that remains uninfected after the [Zika] epidemic," said Alex Perkins.

Perkins is one of the researchers who took part in the study. He added the epidemic will die off before it can infect everyone.

There is currently no vaccine to protect people against Zika virus. The World Health Organization declared the virus a public health emergency earlier this year.

I'm Marsha James

Jessica Berman wrote this story for VOA News. Jim Dresbach adapted it for Learning English. George Grow was the editor.