Certain mosquitoes carry the Zika virus, which has spread rapidly in Latin America. Doctors can’t prescribe medicine to prevent the virus, but several organizations have started testing vaccines on humans. (Felipe Dana/AP)

There’s good news on combating Zika, a virus carried by mosquitoes that has spread throughout Latin America and the Caribbean. A promising vaccine effective in monkeys is being fast-tracked for testing on humans.

A Zika virus vaccine earlier found to work in mice is effective against Brazilian and Puerto Rican strains of the virus in monkeys, too, researchers from the Walter Reed Army Institute of Research and Harvard Medical School reported in a study published Thursday in the journal Science.

The success in monkeys, “brings us one step closer to a safe and effective Zika vaccine,” said Dan Barouch, a doctor at Beth Israel Deaconess Medical Center in Boston. “But of course, there’s a lot more work to do.”

The first phase of testing of the vaccine on humans is expected to start in October.

Two other Zika vaccines are in the human testing phase. Inovio Pharmaceuticals announced last week that it had injected its first participant. The National Institute for Allergy and Infectious Diseases (NIAID) said Wednesday that its vaccine began human testing this week.

The Zika virus typically causes only mild symptoms, such as fever, headache and a rash. But women who have been infected with Zika during pregnancy sometimes have babies with microcephaly (pronounced my-kroh-SEF-uh-lee), a condition in which the infant has an unusually small head. Children with microcephaly often have problems with speech, movement and balance.

“A safe and effective vaccine to prevent Zika virus infection and the devastating birth defects it causes is a public health imperative,” NIAID Director Anthony S. Fauci said in a statement Wednesday.

The threat of contracting Zika has led for some athletes to skip the Summer Olympics in Rio de Janeiro, Brazil. But Zika appears to have spread to the mainland United States, too; officials believe several cases in Florida were transmitted by mosquitoes there.

It’s not known when any of the vaccines could be prescribed by doctors, but Fauci estimated that it would be 2018 or later.