Even as American hospitals prepare for new cases of Ebola, they must brace for a more familiar invader. The flu season will arrive soon — although exactly when, scientists cannot say.

Unlike Ebola, the influenza virus is truly airborne. And if recent history is any guide, it will kill thousands in the coming months.

Flu viruses and Ebola viruses take different routes to the same biological goal: to get into new hosts and replicate. Scientists have learned a great deal about the devious ways in which they manage to do it.

Yet misconceptions about how they travel continue to circulate, including the persistent notion that Ebola, like influenza, is airborne. The uncertainty only grows when possible new cases are identified, as happened on Thursday in New York.