Welcome to the fourth episode of Penn Talks Science for our theme “Vaccines”. Dr. Damon Centola joins us to discuss vaccines in the context of social networks and behavior change. Our interview with Dr. Centola was recorded in April 2021. This episode was created in cooperation with the Science Diplomacy Branch of PSPDG. To learn more about Dr. Centola's work, please refer to the following sources: Change: How to Make Big Things Happen. https://ndg.asc.upenn.edu/book/change-how-to-make-big-things-happen/; How Behavior Spreads: The Science of Complex Contagions. https://doi.org/10.2307/j.ctvc7758p; The Complex Contagion of Doubt in the Anti-Vaccine Movement. https://ndg.asc.upenn.edu/experiments/vaccine-hesitancy/