Covid-19 Booster Shot to Be Offered to Americans Fully Vaccinated With Pfizer, Moderna

The Biden administration on Wednesday called for a third Covid-19 shot starting in the fall for Americans who were fully vaccinated with the two-shot regimen, citing the threat from the highly contagious Delta variant and heightened concerns over data showing initial immunity wanes over time.

The announcement on Wednesday means that booster shots will soon be available for the more than 155 million people in the U.S. who have been fully vaccinated with messenger RNA vaccines from Pfizer Inc. and partner BioNTech SE or from Moderna Inc.

The booster shot would be administered about eight months after the second...