FDA authorizes fourth Pfizer and Moderna Covid vaccine doses for people age 50 and older

The Food and Drug Administration has authorized fourth Pfizer and Moderna Covid vaccine doses for everyone age 50 and older, amid uncertainty over whether an even more contagious version of omicron will cause another wave of infection in the U.S. as it has in Europe and China.

The FDA also said it authorized a second Pfizer booster shot for people age 12 and older who have compromised immune systems, and a second Moderna booster for adults ages 18 and older with compromised immune systems. All of the new boosters are to be administered at...