Researchers and activists in the trenches of the long fight against H.I.V. got a rare piece of exciting news this week: Results from a large clinical trial in Africa showed that a twice-yearly injection of a new antiviral drug gave young women total protection from the virus.

The randomized controlled trial, called Purpose 1, was conducted in Uganda and South Africa. It tested whether the every-six-months injection of lenacapavir, made by Gilead Sciences, would provide better protection against H.I.V. infection than two other drugs in wide use in high-income countries, both daily pills. The results were so convincing that the trial was halted early at the recommendation of the independent data review committee, which said all participants should be offered the injection because it clearly provided superior protection against the virus... Read More