NEW YORK (AP) - Pfizer announced Thursday that it has begun studying a third dose of its COVID-19 vaccine, part of a strategy to guard against mutated versions of the coronavirus.Health authorities say first-generation COVID-19 vaccines still protect against variants that are emerging in different parts of the world.
But manufacturers are starting to prepare now in case a more vaccine-resistant mutation comes along.RELATED: Pfizer's COVID-19 shot is 92% effective at reducing severe illness, 'real world' mass vaccination study findsPfizer said it will offer a third dose to 144 volunteers, drawing from people who participated in the vaccine’s early-stage U.S.