  The COVID-19 pandemic, which began in December 2019, progressed in a
complicated manner and thus caused problems worldwide. Seeking clues to the
reasons for the complicated progression is necessary but challenging in the
fight against the pandemic. We sought clues by investigating the relationship
between reactions on social media and the COVID-19 epidemic in Japan. Twitter
was selected as the social media platform for study because it has a large user
base in Japan and because it quickly propagates short topic-focused messages
("tweets"). Analysis using Japanese Twitter data suggests that reactions on
social media and the progression of the COVID-19 pandemic may have a close
relationship. Experiments to evaluate the potential of using tweets to support
the prediction of how an epidemic will progress demonstrated the value of using
epidemic-related social media data. Our findings provide insights into the
relationship between user reactions on social media, particularly Twitter, and
epidemic progression, which can be used to fight pandemics.
