If you have unprotected sex with a person who has AIDS, you can become infected. HIV infection can be avoided if HIV blockade is administered promptly after high-risk behavior. It is recommended to take the blocking medication within 2 hours of the risky behavior to maximize the blocking effect. If it is more than 2 hours, taking the blocking medication within 48 hours is also more effective. If it is more than 48 hours, taking the blocking medication within 72 hours will certainly hopefully lead to successful blocking, and it is basically ineffective to take the blocking medication more than 72 hours later. So one should be clean and try to use condoms to protect themselves.