One mask is good, and two masks may be better, the Centers for Disease Control and Prevention has said, echoing the same guidance from experts in recent weeks to prevent the spread of Covid-19.

A cloth mask layered over a disposable mask can boost protection. Or, make a mask more snug with the “knot and tuck” method. (See the Q&A below for steps, a visual guide and tips to make two masks more comfortable.)

Masks protect other people —and the wearer — from airborne particles. Because the coronavirus spreads through the air, restaurants and other businesses are increasingly using a trick to monitor circulation. Measuring carbon dioxide (the gas everyone exhales when breathing) can be a good proxy for air flow.

The pace of vaccinations is exceeding President Biden’s December pledge of 100 million shots in 100 days. But even as the distribution reaches 1.5 million a day, that may not be enough. To curb the rise of concerning variants, vaccine distribution must go even faster, public health experts said. Variants with alarming mutations dimmed the hopes of eliminating the coronavirus. As it lingers, though, its threat will diminish, immunology researchers predict. In its endgame, this pathogen might resemble something like the flu or the common cold.