But the new coronavirus attacks the lungs, and in about 20% of patients, infections can get more serious. As the virus enters lung cells, it starts to replicate, destroying the cells, explains Dr. Yoko Furuya, an infectious disease specialist at Columbia University Irving Medical Center.

“Because our body senses all of those viruses as basically foreign invaders, that triggers our immune system to sweep in and try to contain and control the virus and stop it from making more and more copies of itself,” she says.

But Furuya says that this immune system response to this invader can also destroy lung tissue and cause inflammation. The end result can be pneumonia. That means the air sacs in the lungs become inflamed and filled with fluid, making it harder to breathe.