ROBERT SIEGEL, HOST:
One of the best ways to understand Zika virus might be to inject it into volunteers. That sounds crazy, but it's not unprecedented. NPR's Nell Greenfieldboyce explains that researchers are hoping that this approach could help speed up the search for a vaccine.
NELL GREENFIELDBOYCE, BYLINE: The National Institutes of Health in Maryland has a vaccine research center. In a lab there, a scientist named Wing-Pui Kong opens a freezer. He takes out some vials filled with a clear liquid.
WING-PUI KONG: So those are the DNA that we made.
GREENFIELDBOYCE: These vials of DNA are potential vaccine against Zika.
KONG: Which one is the best one? We are testing it in animal, using that to select our top candidate.
GREENFIELDBOYCE: A vaccine made from DNA is just one of the strategies being pursued against Zika. A bunch of other groups are working on different ideas. When will we know if one of them can really protect people? Barney Graham is deputy director of the NIH vaccine research center. He says no one can say for sure.
BARNEY GRAHAM: Most vaccine development efforts are measured in decades.
GREENFIELDBOYCE: New technology does make it much easier to quickly develop a vaccine concept.
GRAHAM: But you can't really have it for public use and distribution until you're able to prove efficacy. Proving that a vaccine works often takes very large organized field trials.
GREENFIELDBOYCE: Those field trials are difficult, time-consuming and sometimes just impossible. Remember Ebola? By the time an Ebola vaccine was ready to go into a large study, the outbreak in West Africa was winding down. Not enough people were being exposed to Ebola to prove that a vaccine could protect them.
What's more, when researchers do manage to do a big clinical trial, it frequently reveals that their vaccine is a dud. So to see if a potential Zika vaccine works, scientists are exploring one option that may seem a little far out. Graham says they'd like to give volunteers a candidate vaccine and then later inject Zika virus into them to see what happens. That could give you real answers fast.
GRAHAM: The limitations would be - you'd have to do this in young people who were volunteering to do this and who were not going to get pregnant.
GREENFIELDBOYCE: In some ways, this is a blast from the past. In the 1950s, soon after Zika was discovered, one intrepid scientist injected it into his arm to see if it could make people sick. He just got a slight fever. After all, if you're not pregnant...
ANNA DURBIN: Zika itself is a pretty mild illness.
GREENFIELDBOYCE: Anna Durbin is an expert on vaccine clinical trials at Johns Hopkins University. She says this fall, we'll likely see safety tests of potential vaccines in about 20 to 50 people here in the U.S.
DURBIN: And then the big question is, what is our next step?
GREENFIELDBOYCE: She says ideally, researchers could compare two groups - people who get the virus alone to people who get a candidate vaccine and then the virus later on.
DURBIN: You know, we would admit them to our inpatient unit where they have 24-hour care.
GREENFIELDBOYCE: Her group has already done this kind of study to evaluate a potential vaccine for a closely related virus, dengue. Dengue can cause serious illness, but one particular dengue virus just causes a rash. And people agreed to be injected with it. That let Durbin and her colleagues show that the dengue vaccine really seemed to work.
DURBIN: We would like to develop a similar model for Zika.
GREENFIELDBOYCE: But here's her concern. Besides the birth defect known as microcephaly, Zika may be linked to Guillian-Barre syndrome. That a disorder in which the immune system attacks the nervous system.
DURBIN: We do not want to put people at risk for that because these are normal, healthy people.
GREENFIELDBOYCE: It's still unclear how often Guillian-Barre actually happens with Zika. That's something scientists are trying to understand now to help them figure out whether it would be ethical to ask people to take a shot of Zika virus to help search for a vaccine. Nell Greenfieldboyce, NPR News.