They found significant and complex immune responses in the people who got sick and the people who didn’t. Scientists noticed changes in their blood 36 hours before some people actually felt sick. Although they understand that some people’s immune systems resist the virus, they still don’t know how or why that happens.

“There is a behind the scene active immune response even when you don’t get sick,” Hero says. “What we found were differences in their biological metabolism and gene expression. These differences had to do with antioxidants.”