(CNN) - There may be a glimmer of hope in the fight to protect people from HIV-1, the most widespread type of the virus and the one that causes the most disease globally.
A new vaccine appears to be safe and induced an immune response in humans and rhesus monkeys in an early stage trial, according to new research published Friday in the journal The Lancet.
That means it's safe enough to go into the next phase of testing, which involves a larger number of humans. It's one of only five experimental HIV-1 vaccine concepts that have gotten this far during the 35 years of the HIV pandemic.
With 1.8 million new cases of human immunodeficiency virus every year, according to United Nations estimates, and almost 37 million people living with HIV worldwide, the quest for a vaccine has been urgent -- and extremely difficult.
Scientists use these initial phases of clinical trials to determine the best dosage to use and to see whether a vaccine is safe.
The new vaccine was tested in 393 healthy people considered at low risk for infection and 72 rhesus monkeys. The human trial participants came from 12 clinics in South Africa, east Africa, Thailand and the United States.
In addition to being well-tolerated by all the test subjects and inducing an immune response against HIV in humans, the vaccine provided 67% protection against infection from the simian-human immunodeficiency virus in the rhesus monkeys. It's unclear whether it would provide protection in humans.
Because this phase of the trial was considered successful, the vaccine can be be tested in a wider patient population that is at higher risk of infection. That trial started in the fall and is underway in 2,600 women across sub-Saharan Africa.
Researchers caution that the results of the early trial do not mean a viable vaccine. The ability to induce HIV-specific immune responses does not necessarily mean the vaccine will protect humans from HIV infection.
"I would say that we are pleased with these data so far, but we have to interpret the data cautiously," said study co-author Dr. Dan H. Barouch, a principal investigator on the study, a professor of medicine at Harvard Medical School and the director of the Center for Virology and Vaccine Research. "We have to acknowledge that developing an HIV vaccine is an unprecedented challenge, and we will not know for sure whether this vaccine will protect humans."
Only four vaccine concepts have made it to testing in humans, and only one provided any evidence of protection in an efficacy trial, but the effect was considered too low to make it available for use.
The new vaccine proved to be protective in monkeys, and while antibodies against HIV were generated in humans, it is unclear whether the vaccine will protect against infection.
"It's a very interesting study. Obviously, the search for an HIV vaccine is very elusive," said Dr. Carlos del Rio, who was not involved with the study but has done similar research as the co-principal investigator of the Emory-CDC HIV Clinical Trials Unit. His unit is one of 37 clinical trials units responsible for implementing the scientific agenda of the National Institutes of Health's international HIV/AIDS Clinical Research Network.
"Despite all the advances we have had with HIV, we need a vaccine. It is critical, and this new vaccine, while there is a long way to go, it is nice to see robust evidence to move on to the next phase of testing."
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