Disruptions resulting from an epidemic might often appear to amount to chaos but, in reality, can be understood in a systematic way through the lens of "epidemic psychology". According to the father of this research field, Philip Strong,  not only is the epidemic biological; there is also the potential for three social epidemics: of fear, moralization, and action. This work is the first study to empirically test Strong's model at scale . It does so by studying the use of language on 39M social media posts in US about the COVID-19 pandemic , which is the first pandemic to spread this quickly not only on a global scale but also online.We identified three distinct phases , which parallel Kuebler-Ross's stages of grief . Each of them is characterized by different regimes of the three social epidemics: in the refusal phase, people refused to accept reality despite the increasing numbers of deaths in other countries ; in the suspended reality phase (started after the announcement of the first death in the country), people' s fear translated into anger about the looming feeling that things were about to change ; finally , in the acceptance phase (started after the authorities imposed physical-distancing measures ), people found a "new normal" for their daily activities.  Our real-time operationalization of Strong's model  makes it possible to embed epidemic psychology in any real-time model (e.g., epidemiological and mobility models).
Disruptions resulting from an epidemic might often appear to amount to chaos but, in reality, can be understood in a systematic way through the lens of "epidemic psychology". According to Philip Strong, the founder of the sociological study of epidemic infectious diseases, not only is an epidemic biological; there is also the potential for three psycho-social epidemics: of fear, moralization, and action. This work empirically tests Strong's model at scale by studying the use of language of 122M tweets related to the COVID-19 pandemic posted in the U.S. during the whole year of 2020. On Twitter, we identified three distinct phases . Each of them is characterized by different regimes of the three psycho-social epidemics. In the refusal phase, users refused to accept reality despite the increasing number of deaths in other countries . In the anger phase (started after the announcement of the first death in the country), users' fear translated into anger about the looming feeling that things were about to change . Finally , in the acceptance phase , which began after the authorities imposed physical-distancing measures , users settled into a "new normal" for their daily activities. Overall, refusal of accepting reality gradually died off as the year went on, while acceptance increasingly took hold. During 2020, as cases surged in waves, so did anger, re-emerging cyclically at each wave. Our real-time operationalization of Strong's model is designed in a way that makes it possible to embed epidemic psychology into real-time models (e.g., epidemiological and mobility models).
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