The first experimental Zika virus vaccine can start being tested in people, the company that makes it said Monday.
The company, Inovio, says it has a go-ahead from the Food and Drug Administration to try the vaccine in people to see if it's safe.
A vaccine that would protect people from Zika infection is still months or, more likely, years away, but this is the first step to getting one for the market. Federal government researchers say they're not far behind with several vaccines they are working on, also. One should be ready for human testing within a few weeks, said Dr. Tony Fauci, head of the National Institute for Allergy and infectious Diseases.
"I just heard that we will likely start at the end of August," Fauci told NBC News.
Inovio's vaccine uses two new technologies: synthetic pieces of DNA, and a new delivery system that uses an electric pulse to open up immune cells so they take up the vaccine better.
"We plan to dose our first subjects in the next weeks and expect to report phase I interim results later this year," Inovio CEO J. Joseph Kim said in a statement. A Phase I trial doesn't usually provide much information on how well or even whether a new drug or vaccine works. Such trials are meant only to show a new product is safe in people.
Tests in monkeys showed the vaccine stimulated an immune response that should protect against infection.
The vaccine also uses a new approach to stimulating the immune system against Zika. The oldest vaccines use a whole bacteria or virus, usually weakened or killed, to get protection.
Newer vaccines have been designed using only the most important parts of a microbe, and labs have been paring those parts down to DNA. Inovio's vaccine uses an artificial DNA sequence inserted into a piece of genetic material called a plasmid, which is like a little package that's easily taken up by cells.
Zika's spread fast across Latin America and the Caribbean. While the virus usually only causes a mild infection, and often no symptoms at all, it causes severe birth defects if a pregnant woman becomes infected.
Microcephaly, a smaller-than-normal head caused by extreme brain damage, is the most obvious, but doctors are reporting a range of other brain injuries caused by the virus, as well as miscarriages and stillbirths.
Like many other infections, Zika can also cause rare side-effects in some people, such as the paralyzing Guillain-Barre syndrome.
Health officials are warning pregnant women or those who might become pregnant to stay out of Zika-affected areas. Some officials are advising women living in Zika-hit countries to put off pregnancy for a while if they can.
But birth control is not always available and women may not be able or willing to delay pregnancy.
So a vaccine is considered important.
Related: Could We Have a Zika Vaccine Soon?
It may be tricky to make one, however. Zika is a very close relative of dengue virus. Researchers have spent years trying to develop a good vaccine against dengue.
That's because there are four strains of dengue. And dengue does strange things to the immune system. Infection with one strain, the first time, usually causes only mild symptoms. But when people are infected with other strains later, they can develop a severe and sometimes deadly immune response.
Doctors worry that vaccination might cause similar effects and one dengue vaccine did seem to make children under nine more likely to become infected and seriously ill with dengue.
The quickest route to a Zika vaccine could be to add on a Zika component to a four-strain dengue vaccine, but there are some fears that the Zika vaccine component might cross-react with the dengue component in some unexpected way.
An experimental dengue vaccine is now being deployed in Brazil for testing in 17,000 volunteers.
Fauci said four more government-sponsored Zika vaccines are also nearly ready for testing. "They are all staggered by a month or two," he said. Each one uses a slightly different approach, but the schedule means six vaccines could be in early human testing by the beginning of next year.
"It's all good news," he added. "It shows the field is robust and a lot of people are involved in it."