[BorisVSchmid]

Not a bad first impulse :-). It often pays in science to wait a few years/follow-up studies before fully accepting something. What is thought to be true in plague is especially fluid now with ancient DNA studies on human remains coming out regularly, each with its own narrative on how to explain the phylogenetic tree.

That said, there are some long-standing questions in plague research, one of which is why the first and second plague pandemic were that much more lethal than the third plague pandemic. Prior to the aDNA work, people speculated that medieval plague was a different pathogen altogether, but that hypothesis has been put to rest now. An alternative theory has been that plague could spread through human ectoparasites, and we found a novel way to test that theory. That resulted in this paper.

[idanman]

Could it be that by the third plague more people developed immunity and therefore less were killed.

[geezerjay]

> more people developed immunity

Better yet, those who survived prior plagues were more likely to already be immune to the disease, and evolutionary pressure led to a more resilient population against this type of disease.

[BorisVSchmid]

Potentially, but I am a bit sceptical. Plague reached a lot of new territory during the third pandemic (for example, australia and the americas), while still having a low mortality. One could check whether native populations to those continents were especially hard hit compared to people from European descent. I haven't heard anything like that.