Giving daily HIV drugs to healthy gay men has huge potential to help reverse the epidemic, say scientists.
The medication prevents new infections by killing the virus before it has a chance to take hold in the body.
Calculations, published in the Lancet, indicate giving the drugs to the most at-risk men could cut new infections by more than 40% in the UK.
Experts said the approach was of “huge benefit” to at-risk men and should be adopted.
Men who have sex with men are at high risk of contracting HIV.
In London, one in eight gay men has HIV, while the proportion in the rest of the UK is one in 26.
While condoms are an effective barrier to HIV transmission, messages to use themare often ignored.
Last year, a UK test on 500 men assessed the impact of an alternative approach called pre-exposure prophylaxis (Prep).
It indicated one case of HIV could be stopped for every 13 men given anti-HIV drugs for a year.
Scientists at the London School of Hygiene and Tropical Medicine modelled the impact of introducing such a treatment across the UK.
They estimated there would be 16,955 new cases of HIV in gay men by 2020.
But giving Prep to the most sexually active 25% of gay men would prevent 7,399 infections (44%).
Dr Narat Punyacharoensin, one of the researchers, said a focus on regular HIV tests and condom use “have been falling short”.
He told the BBC News website: “Prep has a great potential to achieve a level of prevention that could never be achieved by all other HIV interventions.”
He said the cost-effectiveness still needed to be determined, but “pre-exposure prophylaxis offers a major opportunity to curb new infections and could help reverse the HIV epidemic among men who have sex with men in the UK”.
Concerns had been raised that men given the drug would adopt riskier behaviours including stopping using condoms.
But the test on 500 men, which concluded last year, found no difference in levels of other sexually transmitted infections such as chlamydia.
Prof Sheena McCormack, who led that study at the Medical Research Council Clinical Trials Unit at UCL, told the BBC: “[It] demonstrated a huge benefit from adding Prep to the existing risk-reduction package for men who have sex with men.
“This publication endorses the impressive longer term impact that Prep could have on the HIV epidemic among men who have sex with men in this country, and hopefully will guide NHS England towards a favourable decision.”
Dr Michael Brady, the medical director of the Terrence Higgins Trust, said: “This study is really important as it demonstrates that, in a relatively short space of time, Prep could have a dramatic impact on reducing HIV transmissions.”
The NHS is evaluating whether Prep should be offered.
Credit James Gallagher, Health editor, http://www.bbc.com/news/