U.S. regulators cleared giving a third Covid-19 vaccine dose to people with weakened immune systems in an effort to improve protection for those with impaired responses to standard shots. The authorization applies to both Moderna Inc. and Pfizer Inc., with organ transplant recipients or those whose immune systems are similarly compromised covered, the U.S. Food and Drug Administration’s said in a statement late Thursday. Other fully vaccinated individuals don’t need an additional dose right now, the FDA said. Bolstering the agency’s move was a study published in the New England Journal of Medicine on Wednesday ... (full story)