A human study of Zika virus vaccine could begin as early as this year, U.S. health officials told reporters Thursday.
But the officials cautioned that it could be years before the vaccine is available for wide use.
The news came as the Zika virus continues to spread through the Americas. Still, a large outbreak is seen as unlikely in the U.S.
"There's still a lot we don't know, so we have to be very careful about making any absolute predictions," says Dr. Anthony Fauci, head of the National Institute of Allergy and Infectious Diseases. In a briefing for reporters, he added that "we still feel it's unlikely ... we'll see wide-scale outbreaks."
That's because the U.S. has seen only limited spread of two similar viruses, dengue and chikungunya, which are also carried by mosquitoes. They have spread widely in nearby countries but mostly appear sporadically in the U.S., mainly when travelers get them abroad and return home.
Nevertheless, the National Institutes of Health and the Centers for Disease Control and Prevention are launching an intense effort to combat Zika, officials said.
The CDC is now requiring all states to report any travelers who bring the virus into the country, says Dr. Anne Schuchat, the agency's principal deputy director.
So far, 31 such cases have been reported in 11 states and the District of Columbia. None of these people is known to have spread the virus.
But 19 cases of the virus have been confirmed in Puerto Rico, Schuchat says, and some of those people had not traveled to countries that have Zika outbreaks. One case has also been confirmed in the U.S. Virgin Islands.
Schuchat acknowledged that "it's possible — even likely — we will see limited Zika transmission in the United States," but she agrees with Fauci that large-scale outbreaks are unlikely in the U.S.
The main reason is that the mosquitoes that spread the virus are primarily found only in Southern states, and the U.S. does a much better job of protecting people from mosquitoes than do other countries, Schuchat said.
That said, the agency would "remain vigilant" for any sustained transmission. "This is a rapidly changing situation," she said.
So CDC is collaborating with the NIH to develop better tests for the virus. The NIH has also issued a call for researchers already receiving funding for work on viruses like Zika to do more research to better understand it.
Work is also underway to try to develop treatments, and the NIH is pursuing two possible strategies for developing a vaccine, Fauci said.
One involves creating a vaccine from a live, but harmless form of the virus. The other, which is probably more promising, involves using DNA from the virus to formulate a vaccine, he said.
That approach produced encouraging early results in the creation of a vaccine against the West Nile virus, Fauci said.
He predicted the work could create a vaccine that might be ready for early testing sometime this year. But, he added, "we will not have a vaccine this year or probably in the next few years."
Nevertheless, the NIH has already started talking with drug companies to help develop a vaccine. "Things are moving rapidly," Fauci said.
At the same time, the Food and Drug Administration has started taking steps to protect the blood supply against the virus, CDC's Schuchat said. The virus seems to remain in the bloodstream "very briefly," she said, perhaps for only about a week.
"FDA is diligently working with its federal partners and with stakeholders, including blood collection establishments and industry organizations, to rapidly implement appropriate donor deferral measures for travelers who have visited affected regions in order to protect the blood supply," FDA spokeswoman Tara Goodin said in an email.
"FDA will also put in place recommendations to help maintain a safe blood supply in United States territories where the virus is present," Goodin wrote. "We cannot speculate on specific implementation timing at this point."
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