Historian William McNeill will assert that the Antonine Plague and the later Plague of Cyprian (251–ca. 270) were outbreaks of two different diseases, one of smallpox and one of measles, not necessarily in that order.

he severe devastation to the European population from the two plagues may indicate that people had no previous exposure to either disease, which brought immunity to survivors.

Other historians believe that both outbreaks involved smallpox.

The latter view is bolstered by molecular estimates that place the evolution of measles sometime after CE 500.