The F.D.A. has authorized additional shots for older Americans and those with certain immune deficiencies. Here’s what scientists know about who needs the doses, and when.
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Aiming to protect Americans who are most vulnerable to the coronavirus, the Food and Drug Administration on Tuesday authorized a second booster dose of Covid vaccine for all adults 50 and older. The agency’s decision comes as a highly contagious Omicron subvariant known as BA.2 pummels Europe and threatens to do the same to the United States.
But the scientific evidence for a fourth dose is incomplete, at best, and researchers do not agree on whether the shots are needed. Here are some factors to…