What we know — and don’t know — about Merck’s new Covid-19 pill

The announcement that a pill from Merck and partner Ridgeback Biotherapeutics kept Covid patients out of the hospital made headlines and moved stocks late last week. But as is so often true when data are released by press release, there are still many questions left unanswered.

Doctors are excited about the medicine, molnupiravir, because a regimen of pills, even one that involves taking several pills twice a day for five days, should be far easier to deliver to patients than current antiviral Covid-19 treatments, which must be given intravenously. But it’s still...