The first preventive pill for HIV has been hailed as a landmark in the fight against AIDS in the United States, but experts say only a small percentage of those at risk will benefit from it.

U.S. health regulators approved Gilead Sciences Inc's Truvada -- already used globally to treat the human immunodeficiency virus -- for preventing the infection in healthy people at high risk of contracting the virus that causes AIDS.

A number of factors will limit the drug's use for preventing HIV, including the fact that in the United States many people most at risk of infection, as well as their sexual partners, do not have consistent access to healthcare. Even for those with coverage, insurance reimbursement for a $14,000-a-year drug is expected to be tricky.

In addition, therapy with the drug would require otherwise healthy young people to take a pill each day, plus show up for HIV testing every three months.

Scientists are exploring a variety of tactics for using AIDS drug formulations to prevent HIV infection, including long-acting injections, gels and vaginal rings.

About 50,000 new HIV infections are reported each year in the United States.

Read more from Reuters.