Virus (HIV-1/HIV-2)
Often for years (chronic stage)
No — manageable with ART (U=U)
No — PrEP available for prevention
HIV (Human Immunodeficiency Virus) attacks the immune system and, without treatment, progresses to AIDS. Modern antiretroviral therapy (ART) allows people with HIV to live long, healthy lives. A key advance: people on effective ART who achieve an undetectable viral load cannot transmit HIV sexually (Undetectable = Untransmittable, U=U). Risk is strongly directional — receptive partners face 3–5× higher per-act risk than insertive partners.
Receptive anal sex — highest per-act risk
Insertive anal sex — lower but significant risk
Receptive vaginal sex
Insertive vaginal sex (lower risk)
Sharing needles or syringes
Mother to child (pregnancy, birth, breastfeeding)
Oral sex — very low risk, especially without ejaculation
Acute HIV (2–4 weeks post-infection): fever, fatigue, swollen lymph nodes, rash, sore throat
Chronic stage: often completely asymptomatic for years
AIDS stage: severe immune deficiency, opportunistic infections
HIV is not curable, but ART suppresses the virus to undetectable levels. People on effective ART have near-normal life expectancy and — under U=U — cannot transmit HIV sexually. Early treatment start improves long-term outcomes.