Results so far suggest that the injectable drug cabotegravir was 89 percent more effective than pills at preventing HIV infection.

Researchers prematurely ended a study after finding that a shot of an experimental drug every two months works better than daily pills at preventing women from contracting HIV from an infected sexual partner.

The news is a boon to AIDS prevention efforts – especially in Africa, where the study took place and where women have few discreet ways to protect themselves from infection.

Results so far suggest that the drug cabotegravir is 89 percent more effective than Truvada pills at preventing HIV infection, although both reduce that risk.

The results echo the results of a similar study announced earlier this year that compared the shots to the daily pills in gay men.

Cabotegravir is being developed by ViiV Healthcare, primarily owned by GlaxoSmithKline, with Pfizer Inc and Shionogi Limited. The study was sponsored by the United States National Institutes of Health (NIH), the Bill and Melinda Gates Foundation, and ViiV. The drugs were provided by ViiV and Truvada’s manufacturer Gilead Sciences.

“This is a big step forward,” said Dr. Anthony Fauci, the leading infectious disease physician at the NIH. “I don’t think we can overemphasize the importance of this study.”

The drug promises to help young women prevent HIV – “those who need it most,” said Fauci.

According to a study director, Sinead Delany-Moretlwe of Witwatersrand University in Johannesburg, South Africa, young women are twice as likely to develop HIV as men in some regions of the world.

“They need discreet options … without having to negotiate with their partners,” to use measures like condoms, said ViiV’s Deborah Waterhouse.

The study enrolled more than 3,200 participants in seven African countries who were randomly given Truvada pills either every two months or daily. Independent observers advised discontinuing the study after it was found that only 0.21 percent of the women who received the shots had the AIDS virus, versus 1.79 percent of the women who took the pills.

There were more side effects, mostly nausea, with the daily pills.

The makers of cabotegravir are asking regulators for approval to sell it for this purpose, and Truvada is already widely available.

“The urgent work now” is to make all prevention drugs affordable and widely available, said Mitchell Warren, director of AVAC, formerly known as the AIDS Vaccine Advocacy Coalition, a nonprofit focused on prevention efforts that were not part of the study played.

Condoms are still widely recommended as they help prevent a wide variety of sexually transmitted diseases, not just HIV.

“People need choices about HIV prevention,” and this offers a new option, Warren said in a statement.