"Treatment as Prevention" is a concept where the use of antiretroviral therapy (ART)
can reduce the viral load in PLHIV to an undetectable level, typically less than 20 copies/ml in Hong Kong. At this level, the virus cannot be transmitted through sexual activity.

The scientific basis of U=U (Undetectable=Untransmittable)


Through three international studies involving a total of 93,880 instances of unprotected sexual activity, it was found that when the viral load of PLHIV was reduced to an undetectable level, their partners did not acquire HIV even without the use of pre-exposure prophylaxis (PrEP). Therefore, statistically, the risk of HIV transmission through sexual activity is zero when the viral load is undetectable.

How long does it take to achieve U=U after starting HIV treatment?


For most PLHIV, their viral load can be reduced to an undetectable level within 1 to 6 months of starting treatment. If the viral load remains undetectable for at least 6 months, the risk of HIV transmission through sexual activity is considered zero.

More information: Hong Kong Society for HIV Medicine
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