Pfizer and BioNTech Studying Third Covid-19 Vaccine Dose to Fight New Strains

Pfizer Inc. and BioNTech SE have begun a study testing in people whether the companies’ Covid-19 shot can provide protection against emerging strains of the coronavirus. The companies said Thursday they have started the small study to see whether a third dose of their authorized Covid-19 vaccine would increase its effectiveness against new variants, such as the strain first identified in South Africa. The approach differs from that of Moderna Inc., which said Wednesday it had made a new vaccine targeting the strain found in South Africa and shipped doses to U.S. government researchers for human testing.