After 30 years of unsuccessful attempts, an HIV vaccine may be within reach. That’s what scientists at Crucell NV of the Netherlands (a subsidiary of Johnson & Johnson) are saying.

Crucell NV has successfully used a vaccine to protect monkeys from contracting its version of the HIV virus, SIV (simian immunodeficiency virus). After combining SIV proteins with different cold and pox viruses, scientists vaccinated monkeys, and then repeatedly exposed them to a genetically different SIV variation.

As few as 12% of monkeys exposed to the virus became infected after the first of six exposures, while monkeys treated with a placebo were infected 75% of the time. Although 12% may not sound like a lot, Crucell NV explained that SIV is nearly 100 times more infections than HIV.

A human trial is being planned by Harvard Medical School and U.S. Military HIV Research Program. The vaccine will be combined with a booster shot developed by the U.S. military and the National Institute of Allergy and Infectious Diseases.