A Tartu-led study dates 75 plague genomes by their place on the family tree

A genome's position on a phylogeny is itself a constraint on its age. Each sample sits below some branch points and above others, and the Tartu group used that structure to narrow the likely dates of samples whose radiocarbon windows ran for many decades, in some cases more than a century ^[13][12].

The refined dates are an output of the tree, not an independent check on it ^[13]. That bears on the study's most specific historical claim. The lineages expanded and split into three branches around 1450 to 1500 ^[7], and the researchers offer the Great Renaissance Drought as one possible factor ^[8]. Both sides of that comparison depend on dates the phylogeny helped produce. Support for a climate effect comes from modern plague systems, where changes in climate can strongly affect outbreaks among the wild rodents that host the bacterium ^[9].

Dr. Marcel Keller, the study's main author, described the problem the method attacks. "With COVID-19, scientists could reconstruct the spread of individual strains extremely well because the genomes came with precise timestamps. For historical pandemics, those timestamps are often missing or may cover more than 100 years, which limits our ability to interpret the genetic data," Keller said ^[11].

Plague's first European wave ran from 1347 to 1353 ^[4]. The Estonian results begin just after it. "We found evidence for repeated introductions of plague into Estonia starting already in the late 14th century and identified several previously unknown genetic lineages, both in urban and rural settings," said senior author Prof. Kristiina Tambets ^[10]. Two introductions a few decades apart can both sit inside a single radiocarbon window ^[12], so counting them depends on dates tighter than radiocarbon supplies.

The re-dated set is 75 genomes, 64 already published and 11 newly sequenced ^[14][17]. Spread evenly over the four centuries the study covers, that is about one genome every five years for all of Europe and the regions around it ^[18]. A date that overlaps a recorded outbreak puts the sample in the right decades; it does not show that the sequenced person died in the epidemic a chronicler wrote down. The announcement from the Estonian Research Council, dated 20 September 2026, says many genomes were linked to outbreaks recorded in historical sources but does not name which ones ^[19][16]. The team calls the work the first systematic attempt to connect nearly all plague genomes available from the fourteenth to eighteenth centuries ^[15].