New York, Feb 23 (IANS): A ring that continuously releases an experimental antiretroviral drug in the vagina may provide a modest level of protection against HIV infection in women, a large clinical trial in four sub-Saharan African countries has found.

"The ASPIRE (a study to prevent infection with a ring for extended use) study is the first to demonstrate that a sustained drug delivery product that slowly releases an antiretroviral drug over time can offer partial protection from HIV," said one of the lead researchers Thesla Palanee-Phillips from Wits Reproductive Health and HIV Institute in Johannesburg, South Africa.

The ring reduced the risk of HIV infection by 27 percent in the study population overall and by 61 percent among women ages 25 years and older, who used the ring most consistently.

These results were published online in the New England Journal of Medicine.

Women accounted for more than half of the 25.8 million people living with HIV in sub-Saharan Africa in 2014.

"To help bring about an end to the HIV/AIDS epidemic, women - especially those in sub-Saharan Africa - need multiple options for HIV prevention," Jared Baeten, professor at University of Washington in Seattle, US.

The ASPIRE study aimed to determine whether the experimental antiretroviral drug dapivirine could safely and effectively prevent HIV infection when continuously released in the vagina from a silicone ring replaced once every four weeks.

The study, which began in 2012, enrolled more than 2,600 HIV-uninfected women aged 18 to 45 years who were at high risk for HIV infection at 15 sites in Malawi, South Africa, Uganda and Zimbabwe.

The women were assigned at random to receive either the dapivirine ring or a placebo ring. No one knew who received which ring until the end of the trial.

All study participants received a package of HIV prevention services at each study visit.

The investigators found that the dapivirine ring reduced the risk of acquiring HIV by 27 percent among all women enrolled in the trial.