Florida reported its first case of a baby born with the birth defect microcephaly, after the child's mother was infected with the Zika virus while pregnant, officials said.
The mother, a citizen of Haiti, contracted Zika in Haiti and came to Florida to deliver the baby, said a statement from Governor Rick Scott's office.
The Florida Department of Health confirmed the case.
Zika is transmitted to people through the bite of infected female mosquitoes, primarily the Aedes aegypti mosquito, the same type that spreads dengue, chikungunya and yellow fever.
Scientists have concluded that infection with the Zika virus in pregnant women is a cause of the birth defect microcephaly and other severe brain abnormalities in babies.
It is also thought that it could cause Guillain-Barré syndrome, a rare neurological disorder that can result in paralysis.
"It is heartbreaking to learn that a baby has been born with Zika-related microcephaly in our state and my thoughts and prayers are with the mother and child," Mr Scott said in a statement.
The Florida governor said he has allocated $26.2 million in state funds for Zika preparedness, prevention and response, as federal funding has stalled in Washington.
"The Olympics will begin in less than 40 days and millions of Americans will travel through our state to and from Brazil, a country where the Zika virus is rapidly spreading, and we must be prepared," said Mr Scott.
Zika can cause microcephaly, a condition in which babies are born with unusually small heads and deformed brains.
Four infants have been born with birth defects related to the Zika virus in the United States, including in Hawaii and New Jersey, according to the US Centers for Disease Control and Prevention.
However, the CDC declined to give a state-by-state breakdown.
Scientists develop two potential Zika vaccines
Scientists in the US and Brazil have developed two potential vaccines for Zika that have provided complete protection from the virus in lab-based tests.
The early stage vaccines have proven successful in protecting mice, but have yet to be trialled in humans.
Nevertheless, the researchers say they are cautiously optimistic that the medicines will prove effective in people.
Last February the World Health Organization declared the Zika outbreak as a public health emergency of international concern.The scientists, led by Professor Dan Barouch of Harvard Medical School in Boston, developed both a DNA-based and a purified inactivated virus version of the vaccine.
When tested on mice they provided complete protection from the illness, with the mice not showing any detectable virus following the exposure.
In both cases a single shot was sufficient to provide the required level of protection.
The level of antibodies required is similar to other vaccines in the flavivirus family, to which Zika belongs.
Scientists say this means that existing vaccine technology should be sufficient to deliver the antibodies into a human's system.
Although many are in development, these early stage vaccines are thought to be the first to have provided that level of effectiveness.
The team says clinical trials of the vaccine candidates now need to happen as quickly as possible, but it cannot give a timeframe as to when that might happen.
The vaccines need to be tested in larger animals first, followed by humans.
Details of the breakthrough were reported in the journal Nature.
The focus of the current outbreak is in Brazil, where 91,387 likely cases of the virus were registered between February and April.
Up to the end of May the number of confirmed cases of microcephaly there was 1,434, with the number of suspected cases under investigation at 3,257.
A number of other countries around the world have also had suspected cases of the virus.