The first vaccine trials against the Zika virus will likely start this fall, federal health officials announced today (March 10).

President Barack Obama has asked Congress to approve $1.8 billion in federal spending to battle Zika virus, but so far, Republicans in Congress have put up a fight, insisting that health officials should use federal money left over from the Ebola crisis, according to USA Today. Officials from the Centers for Disease Control and Prevention (CDC) said in a news briefing today that it will be difficult for vaccine trials to move forward to subsequent stages unless Congress grants the funds needed to fight the disease.

And health officials say using the money earmarked to fight Ebola isn't the answer. "The idea that we should rob Peter to pay Paul and hope that Congress replaces money that's essential to keep America safe is frankly, I think, too dangerous to do," Dr. Tom Frieden, director of the CDC, told reporters, according to The Hill. [Zika Virus News: Complete Coverage of the 2016 Outbreak]

The mosquito-borne virus has sickened thousands of people in South and Central America. Only about 1 in 5 people infected with the virus show symptoms, such as fever, rash and muscle pain, but the disease is thought to be far more dangerous for pregnant women. Mounting evidence suggests that if a pregnant woman is infected with Zika, her fetus may be at increased risk of developing microcephaly and other developmental disorders.

Caring for one child affected by the Zika virus in utero could cost about $10 million over a lifetime, Frieden said.

Scientists are hard at work on a vaccine, but it could take years before a successful Zika vaccine clears Food and Drug Administration (FDA) regulations, Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, told reporters.

"We believe we can get a vaccine," Fauci said, adding that he felt "cautiously optimistic" because scientists have produced vaccines against other flaviviruses, a group that includes Zika, yellow fever, dengue and West Nile.

So far, Phase 1 clinical trials are slated to start by the end of summer or early fall of this year, he said. Phase 1 trials are small, and are held to evaluate whether a treatment is safe, what dosages are best and what side effects participants report.

If the vaccines given in the Phase 1 trial pass muster and can induce an immune response against the virus, then scientists can proceed to Phase 2 by early 2017, Fauci said. But unless Congress approves the funds, health officials may not have enough money to put together a Phase 2 trial right away, and the entire process may take longer to complete, he said.

Furthermore, private pharmaceutical companies may be hesitant to partner with the government if funding isn't certain, Fauci said. This hasn't happened yet, but it has happened to other drug and vaccine development programs in the past, he added. [10 Deadly Diseases That Hopped Across Species]

Puerto Ricans fight Zika

Meanwhile, the CDC is working on other ways to prevent Zika infections in places like Puerto Rico, where the virus is becoming established. The U.S. territory is approaching its rainy season, a time when mosquitoes thrive. Health experts expect that thousands of pregnant women in Puerto Rico will become infected with the virus this year, Friedman said.

The CDC is running several pilot programs that will determine the feasibility of installing window screens on local dwellings. However, many houses have open eaves, and so installing screens on windows would have little or no impact, Friedman said.

Workers are also spraying insecticides to try to diminish mosquito populations, federal officials said.

The United States is also researching the best ways to prevent Zika infections, and health officials plan to gather at the CDC-hosted Zika Action Plan Summit on April 1 to address the upcoming mosquito season, which typically begins in June or July in the United States, Frieden said.

Follow Laura Geggel on Twitter @LauraGeggel. Follow Live Science @livescience, Facebook & Google+. Original article on Live Science.