Americans With Weak Immune Systems Will Get 3 Covid Shots (1)

Americans with weakened immune systems will be allowed to get three shots of Covid-19 vaccine after U.S. regulators authorized giving an extra dose to the most vulnerable people.

The U.S. Food and Drug Administration’s action expands the use of vaccines from Moderna Inc. and the partnership of Pfizer Inc. and BioNTech SE for organ transplant recipients and patients with other conditions like cancer that hobble the body’s natural infection-fighting response. The decision doesn’t apply to other fully vaccinated individuals, the agency said in a statement.

The U.S. is currently facing a surge of infections spawned by the highly ...