Just days after a local outbreak of the Zika virus began in Miami,????? ?????? hd infecting at least 15 people so far, U.S. researchers are moving ahead with the first clinical trial for a potential vaccine.

Yet their progress could quickly hit a wall if Congress doesn't free up more funding to fight the disease, the White House and scientists warned this week.

“The money that we need to fight Zika is rapidly running out. The situation is getting critical,” President Barack Obama said Thursday during a press conference at the Pentagon.

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SEE ALSO: Likely Zika outbreak in Florida marks turning point for the U.S.

In February, the Obama administration asked Congress to set aside $1.9 billion to fund research for preventing and treating the dangerous disease.

President Obama speaks to the media at the Pentagon, Aug. 4, 2016. Credit: Getty Images

But Congress failed to pass an emergency spending bill before breaking for a seven-week recess in mid-July.

In the absence of new spending from Congress, the government has been funding Zika research by tapping into the dwindling dollars that had been intended to go toward additional Ebola work in the wake of the epidemic in West Africa.

The White House and the U.S. Centers for Disease Control and Prevention (CDC) said their remaining Zika funding could vanish by late September without congressional action.

“Zika is a serious threat to Americans, especially babies,” Obama said, urging Congress to, “Deal with this threat. Help protect the American people from Zika.”

Zika is spread through mosquito bites from the Aedes aegyptimosquito and, less commonly, through sex.

via GIPHY

The majority of people infected with Zika often don’t show symptoms, and if they do, the symptoms are often akin to a mild flu or cold.

For pregnant women, however, the risks are more concerning. Zika is known to cause birth defects and brain abnormalities in children whose mothers were infected during pregnancy.

The first Zika vaccine trials in humans

The National Institute of Allergy and Infectious Diseases (NIAID), part of the National Institutes of Health, launched the first phase of its human vaccine trial earlier this week.

Two of 80 volunteers were injected with an investigational DNA vaccine.

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Dr. Anthony Fauci, director of NIAID, said the funding dilemma won’t affect Phase 1 of NIAID’s clinical vaccine trials, which are expected to wrap up in late December.

But Phase 2 of the trials, which could start as early as January 2017, could face substantial setbacks and delays unless Congress approves more research funding soon, he said.

The "Asian Tiger" mosquito, which also carries Zika. Credit: AFP/Getty Images

“When I say we’re going to run out of money soon, I mean really soon,” Fauci told reporters on a Wednesday press call.

“We cannot afford to delay the work needed to develop a safe and effective vaccine to prevent Zika virus infection,” he added.

The Obama administration said this week it has now spent about $201 million of the $347 million it set aside in April to combat Zika.

The CDC has spent about half of its $222 million in available Zika funding and will likely burn through the rest by Sept. 30, the end of the fiscal year.

“I’m puzzled by this. I just don’t understand why we’re not moving on it,” Fauci told Mashablein early June, when Congress was still debating a Zika funding bill.

A physical therapist in Brazil holds an infant with microcephaly, or an abnormally small head. Credit: Getty Images

“I don’t think it’s a lack of perception of the seriousness of the problem,” he added. “I believe it’s a disagreement as to how you go about addressing the problem.”

If NIAID had sufficient funding, researchers would already be preparing for Phase 2 of the vaccine trials by preparing host clinics and hiring and training personnel, he told reporters this week. The second phase could involve between 2,400 and 5,000 volunteers.

A different clinical trial for a different Zika vaccine is expected to start in October.

In a separate development, researchers from the Walter Reed Army Institute of Research and Harvard Medical School announced Thursday that they found a promising vaccine was effective in monkeys.

Aresearch specialist tests body fluids from rhesus macaque monkeys infected with the Zika virus, June 28, 2016 in Madison, Wisconsin. Credit: Getty Images

The purified, inactivated Zika vaccine was effective against Brazilian and Puerto Rican strains of the virus in rhesus monkeys, a primate frequently used in the study of human disease, according to a study published in the journal Science.

Researchers are fast-tracking the inactivated-virus vaccine for human clinical trials, Bloomberg reported.

A batch of the vaccine has already been manufactured. The Army also agreed last month to transfer its vaccine technology to Paris-based drugmaker Sanofi for further development.

U.S. cases are adding up

About 1,800 cases of Zika have been reported in the U.S., including 500 pregnant women, although all of those cases were from travelers returning home after visiting other Zika-affected countries.

Original image has been replaced. Credit: Mashable

The recent infections in Miami mark the first time Zika was found to be transmitted via infected mosquitoes in the continental United States, the CDC confirmed.

The agency on Monday issued a rare travel advisoryfor a one-square-mile area in downtown Miami where the Zika outbreak is occurring.

The CDC also advisespregnant women against traveling to the U.S. territory of Puerto Rico, where nearly 5,500 people have acquired the disease locally.

Mashable science editor Andrew Freedman contributed reporting to this story.