Alpha’s swift success has left scientists wondering how the variant conquered the world. A new study points to one secret to its success: Alpha disables the first line of immune defense in our bodies, giving the variant more time to multiply.

“It’s very impressive,” said Dr. Maudry Laurent-Rolle, a physician and virologist at the Yale School of Medicine who was not involved in the new study. “Any successful virus has to get beyond that first defense system. The more successful it is at doing that, the better off the virus is.”