Zika vaccine shows promise
Set for laboratory trials in humans after success with primates
On the eve of the Olympics’ opening ceremony in Rio de Janeiro, there’s good news on combating the Zika virus: a promising vaccine effective in monkeys and now being fast-tracked for human clinical trials.
A purified, inactivated Zika virus vaccine earlier found to work in mice is effective against Brazilian and Puerto Rican strains of the virus in monkeys, too, researchers from the Walter Reed Army Institute of Research and Harvard Medical School reported in a study out on Thursday in the journal Science.
Phase 1 clinical testing of the vaccine, developed by the Walter Reed Institute, is expected to start in October.
The mosquito-borne Zika virus has been linked to the birth defect microcephaly and has spread throughout the Caribbean and Latin America, prompting some top athletes to pull out of the Olympics. It appears to have spread to the mainland United States, too; officials believe several cases in Florida were transmitted by mosquitoes there.
In the study, the researchers gave eight control-group monkeys sham vaccines and an additional eight the inactivated-virus vaccine.
They also transferred antibodies from the vaccinated monkeys to mice and other monkeys.
Within two weeks, the vaccinated monkeys developed Zika-specific antibodies capable of fighting the disease. Animals given sufficient levels of those monkeys’ antibodies, or titers, were also protected, the researchers found.
Perhaps most striking, immunity required “relatively modest” titers, said co-senior author Dr. Dan Barouch, a Harvard Medical School professor and director of Beth Israel Dea- coness Medical Center’s vaccine research center.
“These titers should be relatively achievable by these vaccine platforms in humans,” he said. “The fact that those antibody titers protect (against the virus) is really the reason why these data are powerful and provide this optimism for the development of clinical vaccines.”
Barouch and a Harvard team developed two other Zika vaccines that the study found effective in monkeys: a DNA vaccine and a recombinant adenovirus vector vaccine. But inactivated-virus vaccines, killed forms of the virus that usually require several doses or booster shots to offer immunity, have traditionally been used against mosquito-borne viruses such as dengue.
“They’ve been proven to be safe and effective and have been licensed by major regulatory agencies,” said senior co-author Colonel Stephen Thomas, a vaccinologist who specializes in such viruses.
DNA vaccines, which use genetically engineered DNA to generate an appropriate immune response, can offer longer-lasting immunity and don’t require booster shots. But they may not be as practical for Zika, said study author Col. Nelson Michael, who co-leads the Walter Reed Institute’s Zika program.
“Early on, (DNA) looks really sexy. But you have to ask yourself the downstream question,” he said, adding that “we’re not here to protect mice, we’re here to protect humans.”
Compared with the DNA vaccine, far less of the inactivated-virus vaccine was needed for it to be effective, he said.
Amonkey had to be given 100 times as much (5 milligrams) of the DNA vaccine as a mouse received, but it needed just 100 micrograms of the inactivated-virus vaccin — 20 times as much as a mouse got.