Q and A


How infectious is HIV with an undetecable viral load or when co-infected with hepatitis B?

How large are the risks of having sexual relations with someone who is HIV positive with an undetectable viral load? Does hepatitis B affect the infectiousness of HIV? How good of an indicator of the lack of infectiousness of HIV is undetectability in blood (given that I’ve read that it may not necessarily mean much about the magnitude of the virus’ presence in semen)?

Thank you so much.


Thank you for your question.

Having unprotected sex with someone who is HIV positive will always carry some level of risk. However, if the positive person has an undetectable viral load in their semen which has been stable for over 6 months then the risk of transmission is extremely low. To get an idea of how low it may help to read the Swiss Statement. This is related to vaginal sex rather than anal sex.

Having hepatitis B does not increase the infectiousness of HIV. Hepatitis B is 50 to 100 times more infectious than HIV and is transmitted in the same way. There are vaccinations against hepatitis B which are free on the NHS in the UK. If you know someone who is at risk of infection through unprotected sex then having the vaccination is highly recommended.

For more information on hepatitis B please follow this link

Viral load in semen can be tested using the same viral load tests that are used for blood, and your hospital could advise on this. The additional safety from testing semen viral load is that approximately 10% of people with undetectable levels in blood, can have detectable levels in semen.


  1. Charlotte Walker

    Lots of things can affect the CD4 count such as stress, exercise, when the CD4 count is taken, underlying infections, age etc. Alcohol and smoking in moderation do not affect the CD4 count. Excessive use of alcohol could have an affect long term.

  2. Janeth

    What other things affect/influence rebound of CD4 rather than HIV?

    Does alcohol and cigarette smocking affect the level of CD4 among HIV positive people?