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Pfizer booster proves effective against Omicron

Preliminary study reveals a 25-fold increase in effectiveness from a third vaccine shot.

a woman administers an injection to a man
A paramedic with Israel's Magen David Adom medical service administers the third shot of the Pfizer-BioNTech Covid-19 vaccine on August 24, 2021 in Holon. Credit: AHMAD GHARABLI/AFP via Getty Images