The tiny air-filled sacs that make up our lungs. Lungs aren’t like big balloons. They’re more like sponges made up of millions of tiny balloons. There are cells in our alveoli that make a protein that lubricates our lungs and keeps them happy. The COVID-19 virus binds to those cells. Researchers think that may be why the virus is so much more severe than the cold-causing coronavirus.

» COVID-19 Glossary