Masks, Covid and What Kind of Mask—What Experts Say

A year after masks began to blossom on the streets of some cities — and not in others — in response to the Covid-19 crisis, guidance over how best to use them continues to change. One of U.S. President Joe Biden’s first acts in office was to break with his predecessor by issuing a nationwide, if limited, mask mandate. Some European governments are requiring medical-grade coverings in public settings in the face of potential surges in cases connected to new variants of the coronavirus that caus