People at considerable risk of developing severe Covid-19, including millions of Americans with compromised immune systems, now have the option of receiving a preventive monoclonal antibody treatment if they have been or are at risk of being exposed to the coronavirus. The FDA’s action on Friday brings hope to the estimated 3 percent of Americans who are immunocompromised … This is the first time an injectable coronavirus antibody treatment has been approved for use as a prevention of Covid after someone has been exposed to the virus.