Explained | Why the US allowed extra Covid-19 vaccine doses for some

Americans at high risk from Covid-19 because of severely weakened immune systems are now allowed to get a third vaccination in hopes of better protection. Here are some things to know.

Americans at high risk from Covid-19 because of severely weakened immune systems are now allowed to get a third vaccination in hopes of better protection, a policy change endorsed Friday by influential government advisers. The Food and Drug Administration ruled that transplant recipients and other similarly immune-compromised patients can get a third dose of either the Pfizer or Moderna vaccine. But the decision offers an extra dose only to those high-risk groups — not the general public.