  While false rumors pose a threat to the successful overcoming of the COVID-19
pandemic, an understanding of how rumors diffuse in online social networks is -
even for non-crisis situations - still in its infancy. Here we analyze a large
sample consisting of COVID-19 rumor cascades from Twitter that have been
fact-checked by third-party organizations. The data comprises N=10,610 rumor
cascades that have been retweeted more than 24 million times. We investigate
whether COVID-19 misinformation spreads more viral than the truth and whether
the differences in the diffusion of true vs. false rumors can be explained by
the moral emotions they carry. We observe that, on average, COVID-19
misinformation is more likely to go viral than truthful information. However,
the veracity effect is moderated by moral emotions: false rumors are more viral
than the truth if the source tweets embed a high number of other-condemning
emotion words, whereas a higher number of self-conscious emotion words is
linked to a less viral spread. The effects are pronounced both for health
misinformation and false political rumors. These findings offer insights into
how true vs. false rumors spread and highlight the importance of considering
emotions from the moral emotion families in social media content.
