Johnson & Johnson’s Vaccine Offers Strong Protection but Fuels Concern About Variants

Johnson & Johnson, the only major drug maker developing a single-dose vaccine for Covid, announced on Friday that its shot provided strong protection against Covid-19, potentially offering another powerful tool in a desperate race against a worldwide rise in virus mutations.

But the results came with a significant cautionary note: The vaccine’s efficacy rate dropped from 72 percent in the United States to 57 percent in South Africa, where a highly contagious variant is driving most cases.