Steven Spencer, 27, tested positive for HIV in December despite taking PrEP pills for five years, before and after sexual encounters as ordered by his doctor.
The drug is more than 99 per cent effective in preventing HIV when taken correctly.
“My diagnosis was a complete surprise and I was in complete shock, as were my doctors,” Mr Spencer said, knowing the chancers were extremely rare.
A Dutch national, and a man from San Francisco, both unnamed, are reportedly among the small group who have reportedly contracted the virus whilst taking the drug.
'In complete shock': Sydney man contracts HIV despite taking PrEP drug https://t.co/Jrs6xULF6c— The Sydney Morning Herald (@smh)22 March 2019
Around half a million people worldwide take the medication, after multiple international clinical trials demonstrated that PrEP effectively prevents HIV transmission.
Mr Spencer chose to share his story as a sexual health and gay community advocate in order to prevent misinformation that could devalue its effectiveness.
Mr Spencer told the Star Observer: “I have been fortunate enough to connect with several of the other men around the world who have become HIV positive while on PrEP.
“I don’t like to use the term “PrEP failure” which is thrown around in these cases, because PrEP is anything but that."
He said: “What happened to me doesn’t change the fact that PrEP is still the most powerful HIV preventative we have ever had.
“It’s protecting hundreds of thousands of people from HIV in an empowering way, alongside effective treatment for people living with HIV.”
Mr Spencer began HIV treatment immediately after his diagnosis and within six weeks achieved an undetectable viral load, which means he cannot transmit the virus to anyone.
“It was one of the toughest periods of my life,” he added.
The 27-year-old said sharing his story, “has turned a process of grief and anguish into an event of celebration – a celebration of my health, a celebration of my community, and a celebration of remaining true to myself.”
Andrew Grulich, head of HIV Epidemiology and Prevention for HIV at the Kirby Institute called the drug’s usage in Australia a “game-changer.”
Kirby Institute data showed HIV infections declined by almost one-third following the drugs trial in New South Wales.
Professor Grulich said: “PrEP only works if it is taken correctly, so non-adherence is certainly a factor in some cases."
“Individuals should remain confident of PrEP’s effectiveness,” he added.