 In particular, two "new" communities have emerged on Reddit: /r/China _flu and /r/Coronavirus . By studying activities and users in these two communities, we provide a characterization of people's responses to COVID-19 on Reddit . First, we find that user activity peaks around March 17, when the World Health Organization (WHO) announced COVID-19 as a pandemic. Shortly after that, the activity levels of both communities have been declining week by week. We further illustrate the central role of these two communities in the emergence of COVID-related communities.
<meaning-changed>  In particular, two "new" communities have emerged on Reddit: /r/China _flu and /r/Coronavirus . By studying activities and users in these two communities, we provide a characterization of people's responses to COVID-19 on Reddit . First, we find that user activity peaks around March 17, when the World Health Organization (WHO) announced COVID-19 as a pandemic. Shortly after that, the activity levels of both communities have been declining week by week. We further illustrate the central role of these two communities in the emergence of COVID-related communities.
 In particular, two "new" communities have emerged on Reddit: /r/China _flu and /r/Coronavirus , emerged on Reddit and have been dedicated to COVID- related discussions from the very beginning of this pandemic. With /r/Coronavirus promoted as the official community on Reddit, it remains an open question how users choose between these two highly-related communities. In this paper, we characterize user trajectories in these two communities in the emergence of COVID-related communities.