From the Introduction: "The measles virus is a 'simple contagion' that is transmitted through contact between an infected person and a susceptible person. When someone who is newly infected becomes contagious, that person can transmit the disease to someone else who is susceptible, who in turn can transmit it to another, and so on. The result: One highly connected person can trigger an epidemic. Information can act like a simple contagion as well. If I tell you recent news about the availability of a new measles, mumps, and rubella (MMR) vaccine, you can easily repeat it to someone who can then repeat it to someone else. Each new contact and repetition leads to more transmission of the information. The result is the same: One highly connected person can accelerate word-of-mouth transmission of news, allowing it to spread 'virally' across a community (Centola & Macy, 2007). But anti-vaccine sentiment is different. It is a 'complex contagion.' Simply hearing a piece of anti-vaccine propaganda does not change a person's beliefs. Rather, people need to be convinced--the hallmark of a complex contagion--through contact with several peers who can reinforce the legitimacy of a point of view. That kind of social reinforcement confers credibility to the idea that vaccines may be harmful (Centola, 2018)."
Annenberg School for Communication, Network Dynamics Group
Network Dynamics Group: https://ndg.asc.upenn.edu/