President Barack Obama is calling for urgent research into developing a vaccine, testing and treatment for the mosquito-borne Zika virus.
"The president emphasized the need to accelerate research efforts to make available better diagnostic tests, to develop vaccines..., and to ensure that all Americans have information about the Zika virus and steps they can take to better protect themselves from infection," the White House said in a statement.
But researchers say a Zika vaccine may take a decade to develop.
The Ebola vaccine was available sooner because years of research had already gone into developing an Ebola vaccine.
American health officials fear the Zika virus could Infect 60% of the U.S. population (200 million people) when mosquito season begins in earnest in the warmer months.
The Aedes species of mosquito in S. America carries the Zika virus -- but the common variety backyard mosquito in the U.S. can also pick up the virus.
The Zika virus is linked to a rare birth defect called microcephaly, a condition that results in babies born with abnormally small heads and brain damage.
The Zika virus has spread to 25 countries. So far there have been no deaths reported. But in areas with widespread outbreaks such as Brazil, nearly 4,000 babies were born with microcephaly.
Officials in El Salvador have taken the unusual step of warning women not to get pregnant until 2018.
The Zika virus causes mild symptoms including low grade fever, rash, red eyes, and joint pain. About 80% of people infected with the Zika virus show no symptoms, making it difficult for doctors to diagnose the virus in pregnant women.
Zika fever is often misdiagnosed for dengue or malaria in developing countries.
Experts are investigating the possibility that the virus can be sexually transmitted. Traces of the virus were found in semen.
Four people in the New York area, one woman in Virginia, and an adolescent girl in Los Angeles have all tested positive for the virus.
At least 2 of the infected people in NY, the woman in Virginia, and the girl in LA contracted the virus while traveling abroad.
None of the infected are pregnant.
A spokeswoman for the Centers for Disease Control (CDC) in Atlanta said the infected Americans pose no risk to others because it is not mosquito season in NY and Virginia.
The World Health Organization (WHO) predicts the Zika virus will eventually spread to all countries and territories in the Americas except Canada and Chile, where Zika-carrying mosquitoes don't live due to the climate.