Drugs to prevent HIV transmission, known as pre-exposure prophylaxis or PrEP, have existed for more than a decade.

But because they typically require taking a daily pill, they have struggled to make a significant dent in global infections.

“This is a historic day in the decades-long fight against HIV,” said Daniel O’Day, Gilead’s chairman and chief executive officer, in a statement.

Lenacapavir, marketed under the brand name Yeztugo, has been shown in clinical trials to reduce the risk of HIV transmission by more than 99.9% in adults and adolescents – making it functionally akin to a powerful vaccine.

But optimism may be tempered by the drug’s expected eye-watering price tag.

While the company has not disclosed specifics, analysts estimate the US launch price could be as high as US$25,000 per year.

Activists are calling for the price to be slashed to US$25 per person annually to help end the HIV pandemic.

The approval also comes as president Donald Trump’s administration has slashed funding for HIV treatment and prevention programmes both overseas and within the US.