RICHMOND, Va. — When tiny glass vials of coronavirus vaccine began rolling off production lines late last year, federal health officials set aside a big stash for nursing homes being ravaged by the virus. Health providers around the country figured as well that it was prudent to squirrel away vials to ensure that everyone who got a first dose of vaccine got a second one.

Two months later, it is clear both strategies went overboard.

A year into the coronavirus pandemic, buying a heavy-duty medical mask online remains downright maddening.

The most coveted mask to keep safe against Covid-19 has been the N95, the gold standard for pandemic protection because of its tight fit and 95 percent efficiency in filtering airborne particles. Then there’s the KN95 from China, a mask for medical workers, which also offers high filtration and is somewhat looser fitting.

But these masks have been far from easy to buy on the internet. When the pandemic hit last year, they immediately became scarce as health care workers and governments rushed to obtain them. The demand was so intense that a gray market sprang up for them.