A third Covid vaccination shot appeared to significantly curb a delta-led surge in cases and prevent severe illness, according to a study in Israel, the first country to offer boosters to seniors.

Twelve days or more after a booster dose of vaccine made by Pfizer Inc. and its partner BioNTech SE, the risk of a confirmed SARS-CoV-2 infection decreased 11.4-fold relative to people given only two jabs, researchers from Israel’s Ministry of Health and key scientific institutes found. A third dose was associated with at least a 10-fold reduction in the risk of falling seriously ill, according to the research released Friday.