Infections start among people at the river’s mouth, and expand exponentially amongst them, until most of them are infected. It also spreads up the river, but only by local contagion, so the number of deaths (and cases) grows linearly according to how far up-river it has spread. This scenario, however, seems nothing like what we would expect in almost all countries.
That doesn’t seem implausible to me, if the epidemic spreads fastest (and therefore first) in densely-connected areas of the social network graph of in-person contacts and mitigation affects those areas of the graph fastest/most. That plus lag from the implementation of mitigation to the results showing up in the case numbers might make growth look approximately linear for a while. Especially when plotted on a linear plot scaled to previous much-faster growth.
That doesn’t seem implausible to me, if the epidemic spreads fastest (and therefore first) in densely-connected areas of the social network graph of in-person contacts and mitigation affects those areas of the graph fastest/most. That plus lag from the implementation of mitigation to the results showing up in the case numbers might make growth look approximately linear for a while. Especially when plotted on a linear plot scaled to previous much-faster growth.