Yamir Moreno

An infection is spreading through a city, and residents are watching each other: some have already been vaccinated, others are hesitant. Every day, they update their decisions — whether to imitate neighbors or friends who support vaccination.

Every group has its unspoken trios: three friends who are always together. And there are pairs that exist on their own. It turns out that how much trios "contain" pairs determines how everything, from a virus to a new idea, spreads through the group. Scientists introduced a measure they call the nesting coefficient.