If you’re worried about the coronavirus and are having trouble getting hold of medical masks, these numbers will explain why: China is the world’s largest producer of them, with a reported daily capacity of 20 million pieces, but by the estimate of its manufacturers domestic demand alone is around 50 to 60 million per day.

No wonder you can’t find medical masks at your local pharmacy.

Some experts doubt the effectiveness of such masks for stopping transmission of the virus, officially named COVID-19. U.S. health officials say the bug spreads mostly between people who are in close contact with each other, and from respiratory droplets when an infected person sneezes or coughs.

“A surgical mask might provide some protection, but it’s going to be very modest,” William Shaffner, a professor of preventative medicine at Vanderbilt University says.