Can a person who is undetectable transmit HIV by vaginal sex?
Can a person who is undetectable transmit HIV to a partner via unprotected vaginal sex?
If your viral load in undetectable, the risk is very low and may even be zero.
This is based on results from the PARTNER study. In this study there were no HIV transmissions after more than 58,000 times when couples had sex without condoms.
This does not mean that it is impossible to transmit HIV with an undetectable viral load but it is very unlikely and the results are strong enough to not have to use condoms for preventing transmission.