Boyz Doc

Boyz Doc: Dr Laura Waters from Mortimer Market Centre: ‘I want to start a relationship with a guy who’s been HIV for over 20 years, do I need PrEP?’

Dear Dr Laura,

I’m 45 years old and HIV negative but I want to start a relationship with a guy who’s been HIV positive for over 20 years. He says his virus is undetectable which I guess means I can’t be infected by him. But I’m worried. Can I go on to PrEP just to be sure? Many thanks.


Hi Eric,

An important question, with a very clear answer! You are absolutely right that if your new partner is HIV-positive and taking treatment with an undetectable viral load there is a ZERO risk of him passing HIV on to you. 

This message of zero risk of transmission, also called “UNDETECTABLE = UNTRANSMITTABLE” or “U=U” has really taken off over the last year or so. It took time for some of the big HIV organisations to feel comfortable saying ZERO but more and more have signed up to this message. It’s really important that clinics use the right language and avoid terms like “incredibly low risk” or “negligible risk” when there is NO RISK!

When I chat to people in clinic many know about U=U already, some are hearing about it for the first time and others have heard of it but aren’t 100% certain they believe it. After years of believing they could pass the virus on to their sexual partners that’s understandable of course; in this situation I find it’s helpful to actually describe the studies that have led to us feeling confident that zero really is zero.

The original trial was in over 1,700 heterosexual couples where one had HIV and one did not. Where the person with HIV was on treatment and with an undetectable virus there were no transmissions to their negative partner. The problem with this sort of trial is there were frequent visits to the clinic and a lot of counselling about risk reduction, including condom use. 

Since then though we have seen three large ‘real life’ studies looking at people with HIV, on treatment and undetectable, and their HIV-negative partners over time. The PARTNER Study recruited more than 1,100 couples (548 heterosexual couples and 340 gay male couples) followed by a study called ‘OPPOSITES ATTRACT’ which recruited 343 gay male couples: if we combine PARTNER and OPPOSITES ATTRACT there were over 40,000 condomless anal sex acts amongst gay men and no transmissions! 

Last year the results of PARTNER-2 were presented – this time they included only gay men and after 783 couples had sex without condoms 77,000 times there were no transmissions. Hearing those numbers can help people feel confident in the message.

If your new partner is your only sexual partner, and he takes his medication regularly, then you do not need pre-exposure prophylaxis (PrEP). If you have condomless sex with other partners who may have HIV, or are living with HIV but not undetectable on treatment, then you should consider PrEP. 

The medication used for PrEP (a single pill containing two HIV drugs called tenofovir and emtricitabine) can be taken daily or before/after sex and, taken properly, is more than 95% effective at preventing HIV transmission. 

PrEP is available in Scotland and Wales; if you live in England NHS England is funding the PrEP Impact Trial. They recently expanded the number of places from 13,000 to 26,000 so even if your local clinic has no spaces right now they may do again soon ( The other options are to buy it yourself on line; is a great resource, and if you can’t afford to buy it you may be eligible for vouchers to use on the iwantprepnow website through Terrence Higgins Trust’s PrEP Access fund; have a look at their website at

Finally, I would not be a good sexual health doctor if I didn’t encourage you and your new partner to both get full sexual health check-ups! U=U for HIV but a check-up for other sexually transmitted infections is a sensible step and, if you’re 45 or younger, you can access vaccination against HPV (human papilloma virus), the cause of genital warts and most cases of anal cancer.

The Boyz Doc is Dr Laura Waters, an HIV and sexual health consultant at the Mortimer Market Centre in central London. Dr Laura answers your questions every week in Boyz. If you have a question for Dr Laura please email her at [email protected]



To Top