Believed to be the first such case, a man sticking to his preventive HIV medication has become infected with the virus. While this highlights the need to not become complacent in the face of positive trial data, the rarity of such an instance still backs the use of these drugs.  

Announced at the 2016 Conference on Retroviruses and Opportunistic Infections, the individual, a 43-year-old gay man who had sex with other men, tested positive for HIV despite taking pre-exposure prophylaxis (PrEP) drugs successfully for one year.

Called Truvada, the PrEP pill is a cocktail of two different antiviral drugs that has been under scrutiny for several years now as a potential preventive measure for high-risk groups, such as gay men or injecting drug users. The idea is that by keeping a high enough level of anti-HIV drugs in the system, the virus is unable to gain a foothold upon entering a susceptible individual, thus representing a barrier to infection.

And trials have been exceedingly encouraging, with studies suggesting that high adherence – taking the pill 4 to 7 times a week – can offer close to 100 percent protection. Though as would be expected, with reduced adherence comes reduced efficacy. But that is where this present case study is surprising – the man had been following his regimen closely.

Not only did his prescription records show that he had been collecting his medication, but blood tests following his diagnosis indicated that he had consistently been taking Truvada in the preceding 1 to 2 months. By looking for the appearance of antibodies against HIV in his blood, the researchers concluded that this timeframe overlapped with the estimated period that he became infected.   

After conducting further analysis of the virus circulating in his system, a low amount of genetic diversity indicated that the source of infection was a single source, rather than multiple individuals. Critically, it was found that the virus was resistant to several different antiviral drugs, representing the most likely explanation for the medication’s failure to protect from infection. With a range of drugs available to tackle HIV, the man is responding to other therapies that his virus has not shown resistance to, Poz reports. 

While clearly effective, this serves as a harsh reminder that taking PrEP does not make you impenetrable. It may offer some slack, but condoms are still a proven method that not only protect against HIV, but other STIs too.