Antiretroviral drugs can protect people from becoming infected by HIV. But so-called pre-exposure prophylaxis, or PrEP, only works if people take pills daily—which studies show they have trouble doing. Now, monkey experiments with an integrase inhibitor that's injected show how a single shot protects them from the AIDS virus for 11 weeks on average. The drug lasts even longer in humans, which may provide a promising new approach to PrEP.

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