  This study examines Facebook and YouTube content from over a thousand news
outlets in four European languages from 2018 to 2023, using a Bayesian
structural time-series model to evaluate the impact of viral posts. Our results
show that most viral events do not significantly increase engagement and rarely
lead to sustained growth. The virality effect usually depends on the engagement
trend preceding the viral post, typically reversing it. When news emerges
unexpectedly, viral events enhances users' engagement, reactivating the
collective response process. In contrast, when virality manifests after a
sustained growth phase, it represents the final burst of that growth process,
followed by a decline in attention. Moreover, quick viral effects fade faster,
while slower processes lead to more persistent growth. These findings highlight
the transient effect of viral events and underscore the importance of
consistent, steady attention-building strategies to establish a solid
connection with the user base rather than relying on sudden visibility spikes.
