Moderna Says Shot Works Against Variants, Developing Booster (2)

Moderna Inc. said its vaccine will protect against two known variants of the Covid-19 virus, but it plans to start human studies of a booster shot for a strain from South Africa that may cause immunity to wane more quickly.

In laboratory tests, Moderna’s vaccine produced antibody protection against the B.1.1.7 strain first identified in the U.K. at levels comparable with older forms of the virus. But against the South Africa variant, known as B.1.351, the neutralizing antibodies produced were six-fold lower, the company said in a statement.

Despite that gap, Moderna’s shot should protect against either strain, according ...