PrEP is believed to be partially behind a recent fall in new cases of HIV among gay and bisexual men in England.
According to Public Health England (PHE), overall there has been an 18 per cent drop in the number of new diagnoses.
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The downward trend was boosted by London, traditionally an area of high prevalence, where new cases among gay and bisexual men fell 29 per cent.
Health officials said the improved picture was due to more regular and frequent testing, as well as quicker diagnosis and treatment.
But the Terrence Higgins Trust, which campaigns on behalf of HIV patients, said access to the controversial new drug PrEP (preexposure prophylaxis), which the NHS has been legally obliged to start funding, would also contribute to the fall in cases.
The medication, which is taken in pill form before sex, reduces the risk of infection by approximately 86 per cent.
It is expensive, however, and other patient groups, such as those with rare cancers, have said funding for their treatments have suffered due to its cost.
PHE's Dr Valerie Delpech said the recent trend “is clear evidence that HIV prevention efforts are working across the United Kingdom.”
However, although the Terrence Higgins Trust welcomed the new statistics, the lobby group cautioned that 42 per cent of people with HIV are still being diagnosed late, reducing the efficacy of treatments.