The protein that the coronavirus uses to attach to human cells has a compact "ridge" that allows it to attach more strongly to human cells than similar viruses, allowing it to infect better and spread faster. The new coronavirus, SARS-CoV-2, attaches to human cells through what's called a "spike protein.” After the spike protein binds to the human cell receptor — a protein on the cell surface that serves as a door into the cell — the viral membrane fuses with the human cell membrane, allowing the genome of the virus to enter human cells.