An experimental vaccine reduced the level of HIV, the virus that causes AIDS, by at least 80 percent in a Brazilian study of 18 infected patients released in the journal Nature Medicine.

Viral loads in all patients fell and stayed low for one year after being inoculated with the vaccine three times in a six-week period, the study said. In eight of the patients, viral loads fell by more than 90 percent, according to the article posted on the journal’s Web site (nature.com).

The patients did not receive any antiviral drugs prior to or during the study, which was conducted by the Federal University in Pernambuco state and sponsored by French medical institutes.

Despite the encouraging results, researchers advised caution about hope for a cure for HIV.

“We should emphasize ... that the efficacy of such a therapeutic vaccine will not be definitively proven until a randomized trial with an appropriate control arm has been performed,” the authors said in the British journal.

The Brazilian government’s AIDS prevention and treatment program has been cited by the United Nations as a model for the developing world because it provides free antiviral drugs for HIV patients.