The Food and Drug Administration (FDA) has approved updated versions of the Covid vaccines with new restrictions, limiting access to specific age groups and individuals with medical conditions. The decision aligns with Health Secretary Robert F. Kennedy Jr.’s goals to limit vaccine availability, which he has long opposed. Preparing a dose of the Moderna Covid booster in Jackson, Miss., in 2,022. The F.D.A.’s new limited authorization covers those from 6 months old who have medical conditions and all people over 65.