I'm unsure about the time scale in question, but something of this magnitude occurred to the indigenous populations of North and Central Americas, with the introduction of urban diseases (smallpox, influenza, chicken pox, bubonic plague, etc.) from Western Europe that they had no prior exposure to.

If you narrow the geographic scope and widen the temporal scope, the tolls were much higher than 50%.

The consequences are difficult to de-correlate from the other effects of colonization, but no it wasn't pretty.