One day in March, Barouch called Michael to ask if they perhaps were working on a Zika vaccine, because he wanted to test more than one kind.
“I said, ‘Are you kidding me?’” Michael says.
So they worked together, and in June, they published results in Nature that their vaccines had worked in mice. And in the new study, published in Science on Thursday, both the whole-kill and the DNA vaccines “provided complete protection” to vaccinated monkeys, the study reads, as did a third kind of vaccine in which you “take a harmless virus and you basically make it a bus by sticking in genes from a pathogen,” Michael says. The unvaccinated monkeys showed traces of the virus in their blood, urine, cerebrospinal fluid, cervical fluid, and rectal fluid up to a week after exposure.
“We showed that the vaccines work in mice—okay, well, they're mice.” Michael says. “Some people conceive of mice as cat food. But the fact that they work in nonhuman primates will really wake the field up, because typically that means, whoa, we’re very close now to potentially work in humans.”
The group plans to start clinical trials in humans in October, on the whole-kill vaccine. There will be four trials—three in the U.S. and one in Puerto Rico. Two will be done by the National Institutes of Health, one by Walter Reed, and one by the Beth Israel Deaconess Medical Center. Michael says they hope to have the results by the end of the year and then move into efficacy studies in Zika-affected areas. This vaccine joins one developed by Inovio Pharmaceuticals, which is moving into trials soon also, as a promising candidate for eventual public use.
Recent research has shown that the Zika virus only has one serotype, which means that even as the virus evolves different strains, these strains should all be closely enough related that one vaccine should be able to protect against all of them. This is different from, say, dengue, which has five different serotypes. Still, developing different types of vaccines offers flexibility—each one has different advantages and disadvantages. For example, the DNA vaccine is easier to make than the whole-kill, Michael says, but it’s more expensive. And the whole-kill is widely-used, so it’s more familiar to manufacturers. This is partly why the whole-kill is the one moving into clinical trials soon. (Inovio’s vaccine is a DNA vaccine.) The Army has also signed an agreement with the pharmaceutical company Sanofi Pasteur, in the hopes that the company can manufacture the whole-kill vaccine at a larger scale.
“Making 1500 doses [for a clinical trial] is one thing, making 1.5 million—there's only a handful of companies in the world that could do that,” Michael says. “The last thing you want is to have a vaccine that you show works in a clinical trial, and then Brazil says ‘Great, we want 200,000 doses,’ and we say, ‘Well you’re going to have to wait 6 months or a year.’ That's really the dilemma right now is how quickly can we translate out-of-phase-one studies into a public-health countermeasure?”