Q and A


Does PrEP reduce risks further when viral load is undetectable?



Most people – including doctors – believe that either one approach or the other would be fine. This is becasue when viral load is undetectable the risk of transmission is virtually zero and this is also the case when PrEP is taken as precribed.

Even when PrEP guidelines try to suggest that condoms should still be used with PrEP, this misses the main reason why people want to use PrEP.

The level of risk from having an undetectable viral load in the PARTNER study is based on the researchers believing that with an undetectable viral load, the risk is actually zero.

Scientifically, you can never prove something cannot happen though. So the best scientific approach is to try to quantify the absolute risk. Defining this risk is the aim of the PARTNER study and the extension study that is enrolling additional gay couples.

In defining risk, scientist also calculate a possible range called the confidence interval. As a study get bigger, with more people over a longer time, exactly the same results produce smaller and smaller confidence intervals – with the risk approaching zero.

I have not heard of any linked transmissions when the positive partner has an undetectable viral load. This might mean the actual risk is zero, or it might happen once in 50,000, or once a million, or once in ten million times. No study will ever show this because it would be too expensive and difficult to run.

See this report to understand this issue and thePARTNER results so far:

The data for someone taking PrEP might be just as good as this, so long as someone takes PrEP every day and waits for a week or two before being at risk.

See recent reports on results of the UK PROUD study and the French Ipergay studies:

This Q&A include information on current UK access and issues to consider:

Most doctors think that either one approach or the other would be fine. Even when PrEP guidelines try to suggest that condoms should still be used, in practice PrEP is highly effective, but then so it having an undetectable viral load.

Everything in life carries some risk. Sometimes it is easier to weigh up risks and then decide whether they are worth taking in order to have a better quality of life and to make life worth living. Every time you get in a car or airplane, you decide a small risk is worth taking to either get somewhere faster or see something that you wouldn’t otherwise see.

The data on dramatically reduced risk from having undetectable viral load or being on PrEP are, for many people, strong enough to balance the genuine better please from not always using a condom. For others, the fear of HIV would never let this happen. So this depends on individual believes and decisions that both you and your partner have to talk about and agree on.

If you decide that treatment is sufficient, then you could also consider joining the PARTNER 2 study so that you can contribute to the data that you really want the research to show.

Good luck with whatever you decide – this might take time – so please find a way that the discussion themselves don’t add pressure to your relationship. You have plenty of time to find what is right for both of you.