U.S. government researchers said on Wednesday they have begun their first clinical trial of a Zika vaccine as concerns over the mosquito-borne virus mount following the first cases of local transmission in the continental United States.

There is no approved vaccine or drug for Zika, a virus spreading rapidly in the Americas that can cause the birth defect microcephaly, marked by small head size that can lead to severe developmental problems in babies.

A number of companies and academic groups are racing to develop a Zika vaccine, which is not expected to be ready for widespread use for at least two to three years.

The National Institute of Allergy and Infectious Diseases (NIAID), part of the National Institutes of Health federal research agency, said its early-stage clinical trial will involve at least 80 healthy volunteers ages 18 to 35 at three study sites. It said the trial will evaluate the experimental vaccine’s safety and ability to elicit an immune system response.

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

U.S. vaccine maker Inovio Pharmaceuticals in June won U.S. Food and Drug Administration approval to begin testing its Zika vaccine in humans. It began its clinical trial last month, aiming to enroll 40 healthy adult volunteers in Miami, Philadelphia and Quebec City.

U.S. concerns over Zika, which is spreading rapidly in the Americas and has hit Brazil the hardest, have increased since Florida authorities last week reported the first signs of local transmission of the virus in a Miami neighborhood. Public health officials have said small, localized outbreaks are likely in southern U.S. states already vulnerable to mosquito-borne disease.

The White House said President Barack Obama spoke by telephone to Florida Governor Rick Scott about the Zika outbreak.

Texas health officials said on Wednesday that they were on high alert for local Zika transmission and urged residents to follow precautions against mosquito bites.

“It’s the perfect mix – local transmission in Florida, travel to Brazil, and we’re at the height of mosquito season in Texas,” said John Hellerstedt, Texas Department of State Health Services commissioner, referring to the Olympic Games beginning this week in Rio.

Fauci said that while it will “take some time” before a vaccine against Zika is commercially available, the launch of the study marked an important step forward.

The study sites for the NIH vaccine trial were: NIH facilities in Bethesda, Maryland; the University of Maryland School of Medicine in Baltimore; and Emory University in Atlanta.

The NIAID said the vaccine approach is similar to one used for another vaccine it developed for West Nile virus. The Zika vaccine includes a piece of DNA that has been engineered to contain genes for proteins of the Zika virus. Such DNA vaccines do not contain infectious material so they cannot cause a person to become infected with Zika, the NIAID said.

Strategies in the Zika Fight

U.S. officials are willing to consider a range of options to control the spread of the Zika virus, the White House said in response to questions about whether it would be willing to relax restrictions on some pesticides.

“We’ll certainly rely on the advice of experts in making decisions about the most effective strategies to deploy to fight the mosquito population,” White House spokesman Josh Earnest told a news briefing.

As with past, high-profile disease outbreaks, a new crop of businesses have begun to tout unproven products that protect against Zika.

New York Attorney General Eric Schneiderman said his office has sent cease-and-desist letters to seven companies accused of deceptively marketing ineffective Zika-protection products. Schneiderman also issued an alert warning consumers against the companies’ advertisements, which mainly promote ultrasonic and botanical oil-based mosquito repellants.

Those products, mostly sold online with some at discount and local stores, “simply don’t work,” Schneiderman told a news conference.

Schneiderman said his office will pursue further legal action if the companies do not respond to the cease-and-desist letters, which warn businesses to halt unlawful activity. He said they were mainly “fly-by-night” operations likely to shut down and pop up elsewhere to evade law enforcement.

“Our first goal is to shut them down,” Schneiderman said.

(Additional reporting by Jessica Dye and Anthony Lin in New York and Doina Chiacu in Washington.)