Several teams of scientists are racing to develop a vaccine for the Zika virus. But what if a drug that already exists could stop an infection in its tracks?

According to new research, it’s not a totally crazy idea.

A group of researchers has identified two dozen Food and Drug Administration-approved drugs that have shown some ability to block Zika from infecting human cells in the lab, according to a paper published Thursday in the journal Cell Host & Microbe. Some of these drugs — which treat infections, cancers, and even depression— also showed potential to prevent infection in certain cells tied to fetal defects in pregnant women.

The research is preliminary and does not have immediate implications for people wanting to protect themselves from a Zika infection. Instead, it provides a winnowed list of drugs to study further, said Dr. Mariano Garcia-Blanco, the paper’s senior author.

“I want to be cautious about this because I don’t want people running to the pharmacy asking for these drugs,” said Garcia-Blanco, a molecular biologist and virologist at the University of Texas Medical Branch at Galveston.

The researchers first screened 774 drugs to see if they could protect isolated human cells from a strain of the virus taken from Aedes aegypti mosquitoes in Mexico. They eventually narrowed the pool to 24 drugs that showed some ability to block Zika from infecting cells.

The 24 drugs now stand as leads for other scientists to study in animals, and eventually people, to see if they are truly effective against Zika, researchers not involved with the project said. Using an existing drug that has already been shown to be safe could expedite the research and regulatory process before it can be deployed, although some of the drugs carry extra side effect risks for pregnant women that need to be considered.

“The search for something that will work against Zika virus infection is so urgent that it makes sense to try existing drugs,” said Lenore Pereira, a molecular virologist at the University of California, San Francisco, who was not involved with the new paper.

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The mosquito-borne Zika virus typically causes only a few days of fever, aches, and rash, if any symptoms at all. But when it infects women who are or become pregnant, it can also infect the fetus and cause serious defects.

Garcia-Blanco said he is now talking with other researchers about the next steps in testing the drugs against Zika, and added that scientists should consider using some of the drugs together because they work in different ways.

The candidate drugs don’t all share certain characteristics, Garcia-Blanco said. While some have shown past hints that they can fight flaviviruses — the virus family that includes Zika — others had never before shown any antiviral ability, according to the study.

When a pregnant woman contracts Zika, it takes some amount of time for the virus to pass from mother to fetus. Scientists are not sure how long they might have, but the hope is that if they hit the jackpot and find a drug that can halt infection — and is safe for pregnant women to take — a pregnant woman could be treated as soon as her infection is discovered, preventing the virus from crossing the placenta or reaching the developing brain. This is a regular practice for preventing HIV from passing from mother to fetus.

“That is a dream, that would be the ideal outcome,” Garcia-Blanco said. “We’re very far from that goal right now, but we’re one step closer because these drugs are already approved.”

“It’s certainly a window of opportunity,” said Pereira, who recently authored a paper about how the virus infects a fetus and that suggested the antibiotic duramycin also reduced Zika’s ability to infect cells.

The scientists did not screen the drugs for their ability to rid cells of existing infection, but beyond studying the drugs in a standard human cell line, they also tested selected drugs on certain kinds of cells that could be involved in the transmission of the virus or how the virus causes fetal defects.

Specifically, they looked at cervical cells (the virus can be transmitted through sex), placental cells, and neural stem cells (which scientists think the virus infects in fetuses, disrupting brain development). They also tested the drugs on a kind of epithelial cell that forms the lining of the amniotic sac and has been found to be infected by the virus.

The scientists discovered that at least a few of the drugs protected all those cells against Zika infection.

Even if scientists identify a drug that stops a Zika infection, this doesn’t mean work on vaccines can stop, said Dr. Dan Barouch, who is working on experimental Zika vaccines and directs the Center for Virology and Vaccine Research at Beth Israel Deaconess Medical Center in Boston. A vaccine could stop the cycle of transmission.

“For Zika virus, there needs to be vaccine development in parallel with drug development,” Barouch said.

Several vaccine candidates are being developed with the idea of wide delivery, starting first with women of child-bearing age and their male sexual partners.