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."
KELLY MCEVERS, HOST:
Health authorities in Brazil announced today they have discovered active Zika virus in saliva and urine. They're telling pregnant women not to share cups or eating utensils with other people and they should be careful about kissing people. But health authorities in the U.S. say there's no evidence that Zika can spread through saliva and urine. Joining us now to talk about all this is NPR health correspondent Rob Stein.
And, Rob, so when the authorities in Brazil say they've found active Zika virus in saliva and urine, what do they mean?
ROB STEIN, BYLINE: Yeah. Well, Kelly, you know, this isn't actually the first time that anyone's found any evidence that Zika can be found in saliva and urine. You might remember there was - the first big outbreak of this virus occurred in French Polynesia a couple years ago. And back then scientists detected evidence of genetic material in people's saliva and urine, but what's different here is scientists in Brazil, they took samples from two infected people, they brought it into the laboratory and they exposed it to cells in the laboratory and showed that the saliva and urine could actually infect cells. And that raises the theoretical possibility that the virus could be spread that way but the emphasis is on theoretical.
MCEVERS: Why is it only theoretical?
STEIN: Well, you know, it's a big jump to go from detecting the virus in saliva and urine to say that you can actually catch it that way. And the reason is it could be lots of reasons why even though it's there, it can't infect anybody. There may not be enough of the virus present or there may be other substances in the saliva and the urine that keep it from infecting other people. So you remember, there, you know, are other viruses that are found in lots of bodily fluids that don't infect anybody with anything. HIV, for example, can be found in saliva and in urine and even tears, but nobody gets AIDS that way.
MCEVERS: All right, but we now know that Zika is not only spread through mosquito bites, right? I mean, there was a case in Dallas of someone who got it through sexual contact so that's obviously a very real risk, isn't it?
STEIN: That's right. The virus has been found in semen in that Dallas case of sexual contact, and that prompted the CDC today to issue advice to pregnant women for how they could protect themselves from getting infected through sexual contact. And what they said, basically, is that if you're a woman who's pregnant and your sexual partner either lived in or has traveled to parts of the world where Zika's spreading, you should either abstain from sex or use condoms every time you do have sex to protect yourself from getting infected. But they stress that the - it's really important to remember the main way Zika spreads is through mosquitoes. That's by far the overwhelmingly dominant way you can get Zika.
MCEVERS: What are they saying about the risk - the wider risk - of the disease here in this country?
STEIN: Well, the CDC and other health officials are saying, you know, look, we have the mosquitoes in this country that spread this virus so there is a possibly that it could start to spread. So far, there's no evidence that that's happened yet. There's been a total of 51 cases confirmed in this country. One of them was this person who got infected through sexual contact. The other 50 - all of them were all travelers who picked it up some place else and then brought it back here.
That said, since the mosquitoes are here, you know, there's a pretty good chance that at some point it probably will spread, but they don't think there's a very good chance that it's going to spread widely. And the reason for that is we do a really good job in this country of controlling mosquitoes, and there've been other diseases - similar diseases like dengue and chikungunya that have come to this country and spread the same way, and there's been a little bit of spread but they've been able to contain those outbreaks really fast.
MCEVERS: That's NPR Health Correspondent Rob Stein.
STEIN: Oh, sure. Thanks Kelly. Transcript provided by NPR, Copyright NPR.