Extended in vivo activity of VRC01 HIV-1 prophylaxis entails initial protective efficacy and subsequent breakthrough infections.

VRC01 prophylaxis maintained 66.3% cumulative prevention efficacy through week 104 against highly sensitive HIV-1 (IC80 < 1 microgram/milliliter), but protection declined after week 80.

• Why it matters: The trials needed to determine whether antibody-mediated prevention with a single broadly neutralizing antibody sustains protection long enough to prevent acquisition and escape.
• What they did: Two parallel AMP efficacy trials assessed HIV-1 acquisition through the week 104 visit, comparing VRC01 versus placebo and tracking diagnosis timing and VRC01 resistance by IC80 thresholds.
• The result: After week 80, HIV diagnoses and VRC01 resistance increased in VRC01 groups versus placebo, including 11 versus 1 diagnoses for viruses with IC80 ≥ 5 microgram/milliliter, implying waning in vivo activity and breakthrough infections.

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