About 175 executives were expected at the Biogen leadership conference on Feb. 26. Employees from Biogen locations around the United States and the world reunited with colleagues they don’t often get to see. Within days, though, the Biogen conference would be infamous, identified as an epicenter of the Massachusetts outbreak of Covid-19, with 70 of 92 coronavirus infections in the state linked to the conference as of Tuesday night, including employees and those who came into contact with them. That doesn’t include a cascade of individual cases in Tennessee, North Carolina, Indiana, New Jersey, Washington, D.C., and Norway, and suspected...