Johnson & Johnson’s Booster Shot Prevents Severe Infection (2)

A booster dose of Johnson & Johnson’s Covid-19 vaccine provided 100% protection against severe disease when given two months after the first inoculation, according to widely anticipated data that suggests it increases the potency of the one-time shot.

The booster was 94% effective at preventing symptomatic Covid infections in the U.S. portion of the Phase III trial, and 75% effective overall when it was given 56 days after the initial dose, the company said in a statement Tuesday. A second study found the additional shot spurred a 12-fold increase in production of antibodies against Covid when it was given ...