No, it's a fudging great magma plume which has historically erupted on a fairly regular basis..... the next one is overdue. It's not a planet killer but the huge amounts of particulates thrown up in to the atmosphere will cause a huge reduction in light levels causing a massive reduction in...
It seems to kill about 50% though, that fact it spreads so fast and needs intensive care in order to have a hope of recovering will drain health services at an alarming rate if it ever gets here.
I think it would be far worse than that. Our creaking NHS would not be able to cope with the huge amount of infected people, throw in the fact that doctors and nurses will be infected too and that will further erode our ability to cope.
Society will effectively collapse as experienced doctors...
With respect, a 1350's virus/bacteria would probably wipe out about 99% of us in this day and age. Thanks to our fast intercontinental links via air travel, a seriously dangerous disease is almost impossible to contain.