The Biden administration is expected to call for a third Covid-19 shot for fully vaccinated Americans with two shots. The administration is worried about the threat from the highly contagious Delta variant and heightened concerns over data showing initial immunity wanes over time. The announcement on Wednesday is likely to cover the more than 155 million people in the U.S. who have been fully vaccinated with messenger RNA vaccines from Pfizer Inc. ($PFE@US) and partner BioNTech SE ($BNTX@Germany) or Moderna Inc. ($MRNA@US). The booster shot would be administered about eight months after the second dose of the vaccine.
