By LAURAN NEERGAARD and MATTHEW PERRONE
WASHINGTON (AP) — With many Americans who got Pfizer vaccinations already rolling up their sleeves for a booster shot, millions of others who received the Moderna or Johnson & Johnson vaccine wait anxiously to learn when it’s their turn. Federal regulators begin tackling that question this week. On Thursday and Friday, the Food and Drug Administration convenes its independent advisers for the first stage in the process of deciding whether extra shots of the two vaccines should be dispensed and, if so, who should get them and when. The final go-ahead is not expected for at least another week.