The flu shot finally gets an upgrade

A scientist works in the lab at the Moderna Inc. headquarters in Cambridge, Massachusetts. | Adam Glanzman/Bloomberg via Getty Images This story appeared in Today, Explained, a daily newsletter that helps you understand the most compelling news and stories of the day. Subscribe here. The Food and Drug Administration approved Moderna’s mRNA flu vaccine this week — a major public health breakthrough for an administration that’s been troublingly down on vaccines.  The flu is a gigantic and…