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FAQ: If your viral load is undetectable, can you still pass the virus to another person through sex?

for Veterans and the Public

Frequently Asked Questions

Q: If taking anti-HIV drugs has made my viral load undetectable (meaning that the virus isn't showing up on blood tests), can I still pass the virus to another person through sex?

The research results available at this time show that our current HIV medication regimens (antiretroviral therapy, or ART) are very, very effective at preventing HIV transmission to a sex partner if the HIV viral load is undetectable. The following two studies focus on this question.

A large international study looked at heterosexual couples in which one partner was HIV positive and the other was HIV negative (we call these serodifferent couples). The study found that if the positive partners took ART to suppress their viral loads, their risk of infecting their partners was enormously reduced, by 93% overall, over about 5 years. And, if the HIV-positive partner was consistently on HIV medications, with an undetectable HIV viral load, there were no partner infections. It is important to note that the couples in this study were encouraged to use condoms.

A smaller study looked at both male-female serodifferent couples and male-male serodifferent couples who did not use condoms (and did not plan to use them). All of the HIV-positive partners in the study were on ART and had undetectable HIV viral loads. After more than a year, none of the HIV-negative partners had become HIV positive.

The results of these studies show that if an HIV+ person is on ART with a completely suppressed HIV viral load, the risk of infecting an HIV-negative sexual partner is likely to be extremely low. However, there are some major caveats to consider:

  • The risk of HIV transmission may be very low if the HIV-positive person's viral load is suppressed, but the opposite is also true: risk may increase substantially if the HIV viral load is not undetectable.
  • Very low risk does not mean zero risk, and ART alone will never be 100% protective for all couples. This is because HIV transmission may occur if patients stop taking their HIV medications, if they miss doses, if their HIV viral loads are not suppressed for other reasons, if they have other conditions that increase the amount of HIV in their sexual fluids (for example, sexually transmitted infections), or they engage in riskier practices.
  • We need more data to be able to specify what the level of risk of HIV transmission is, especially for men who have sex with men and for transgender women and men. This means we will need to study more serodifferent couples for longer periods of time.
  • An HIV-negative person may have a low risk of being infected by a partner who is taking potent ART, but he or she will not be protected from being infected by any other partners who are not taking ART.
  • We have very few data on how effective ART is in preventing HIV transmission via sharing injection drug equipment.
  • And, there is no sure way to know whether we can apply these data to you or to any specific individual.

It is important to ask your health care provider for advice that is targeted to you as an individual, and to your partner, in order to get a better idea of your risk for passing HIV and ways that you might lower this risk. And of course, it is really important to have frank and open conversations about HIV transmission with your HIV negative partner(s), so you and they can make informed decisions about what level of risk you both are willing to accept.

Finally, remember that for ART to be effective, you MUST take your HIV medications every day, as prescribed, in order to keep the HIV virus suppressed to undetectable levels. And ART does not take the place of other risk-reduction strategies, like PrEP for HIV-negative partners, condoms, and behavioral changes--these may be important not just for HIV reduction but also for STD prevention and pregnancy prevention.