Two new vaccines being developed to battle the deadly Ebola virus involved in the current outbreak have passed a critical test, proving effective in animal trials with just one dose and without apparent side effects, researchers say.

The vaccines were tested on 10 macaque monkeys; eight were given the new vaccines while two were left unvaccinated as controls.

When all the macaques were injected with the strain of Ebola virus from the current outbreak, none of the vaccinated monkeys became sick, but the unvaccinated duo died within a week, the researchers report in the journal Nature.

Tests in nonhuman primates, important because they are more closely related to humans than other commonly used lab animals, suggest safety trials using healthy human volunteers could begin early this summer, says study lead author and Ebola expert Thomas W. Geisbert of the University of Texas Medical Branch in Galveston.

"These findings may pave the way for the identification and manufacture of safer, single dose, high-efficiency vaccines to combat current and future Ebola outbreaks," he says.

The new vaccines have been developed from an existing vaccine being tested on Ebola patients in Liberia, which has shown some side effects that include fever and joint or muscle pain.

While those side effects were not considered severe enough to halt its use, they somewhat resemble early symptoms of Ebola, leading to possible confusion over whether a recently vaccinated person still contracted the virus or is just having a reaction to the vaccination.

"I think these improved vaccines should fix that," says Geisbert, noting their apparent lack of side effects in the animal trial.

An interdisciplinary team consisting of researchers from the Texas university and Profectus BioSciences Inc. of Maryland has developed the new vaccines.

Profectus has been given $55 million in funding in recent months to research vaccines for the virus, most of it from a consortium of government agencies including the Department of Defense and the National Institutes of Health.

The new vaccines utilize a virus — vesicular stomatitis, which is not dangerous to humans — that has had a portion of the Ebola virus added to create a "Trojan horse" vaccine that can safely trigger immune responses to Ebola.

In the new research, scientists have targeted the virus version currently circulating in West Africa, identified as West African Makona strain of Ebola Zaire.

"Our findings show that our candidate vaccines provided complete, single-dose protection from a lethal amount of the Makona strain of Ebola virus," says John Eldridge, chief scientific officer-vaccines, at Profectus.

The current outbreak of Ebola infections in West Africa is showing signs of abating, with 30 new confirmed Ebola cases being reported, the lowest weekly total since the third week of May 2014, according to figures tallied by the World Health Organization. However, some 10,572 people have died since cases began appearing in 2014, mostly in Guinea, Liberia and Sierra Leone. That makes finding an effective vaccine a priority.