The Variant Hunters: Inside South Africa’s Effort to Stanch Dangerous Mutations

A few months ago, Sizakele Mathe, a community health worker in this sprawling hillside township on the edge of the city of Durban, was notified by a clinic that a neighbor had stopped picking up her medication. It was a warning sign that she had likely stopped taking the antiretroviral tablet that suppresses her H.I.V. infection.

That was a threat to her own health — and, in the era of Covid-19, it might have posed a risk to everyone else’s. The clinic dispatched Ms. Mathe to climb a hill, wend...