A skeleton buried during an epidemic keeps in its remains the DNA of the bacterium that killed it. Radiocarbon dating says when the person died, but often with a margin of more than a hundred years. For a town struck by plague several times, that margin cannot tell which epidemic it was.
The Black Death reached Europe in 1347 and the first great wave ended in 1353. The disease stayed. For the next four centuries it came back in waves, a period historians call the second plague pandemic. The bacterium is Yersinia pestis. Over a hundred ancient genomes of strains from those centuries have already been reconstructed, and the archives hold a vast body of chronicles and records. Bringing the two sources together is hard, precisely because of the dates.

The paper appeared in PNAS, the journal of the US National Academy of Sciences, on 10 September 2026, open access. It has 25 authors. The first is Marcel Keller, of the universities of Tartu and Bern. Among the others are the historian Philip Slavin, of the University of Stirling, and Kristiina Tambets and Christiana L. Scheib, also at Tartu, who sign as senior authors. The Estonian Research Council press release was republished by ScienceDaily on 20 September.
The team worked on human remains from eleven European sites. It obtained 11 complete genomes and 15 at lower coverage, meaning read less densely and with more gaps. The dates run from 1349 to 1710. The press release places the sites in Estonia, Russia, England, the Netherlands and Switzerland. Italy is not among them.
The core of the work is a dating method. The authors call it phylogenetically informed radiocarbon modelling. Phylogeny is the family tree of the bacterium’s strains, rebuilt from the mutations that accumulate over generations. A genome’s position on the tree shows whether it is older or younger than others. The method sets this information beside the radiocarbon dates of each sample. The intervals shrink, and the abstract speaks of more accurate and more precise dates.

With the narrower dates, the authors link 75 genomes to epidemics recorded in historical sources. The abstract uses a careful adverb, «tentatively». The press release breaks the 75 down into 64 previously published genomes and 11 new ones. The press release speaks of genomes linked to specific waves and outbreaks, and the adverb disappears.
The press release tells more, which is not in the abstract. Around 1450 to 1500 the bacterial lineages are said to have expanded and split into three main branches, perhaps with new reservoirs among wild rodents. The authors reportedly point to the Great Renaissance Drought as a possible factor. Estonia would have been reached several times, from the late fourteenth century. Some new genomes would tie outbreaks to the Thirty Years’ War, between 1618 and 1648, and to the Great Northern War in the early eighteenth century. During the siege of Tallinn in 1710, plague reportedly killed Swedish soldiers, Russian soldiers and civilians. 1710 is also the latest of the new genome dates. The full text was not consulted for this article, and these points remain to be checked.
The ScienceDaily headline speaks of four hundred years of returns. The abstract refers to the four centuries following the Black Death. The new genomes span 361 years.
Dating a genome better helps follow how the bacterium changes over time and how it moves through space. The abstract calls these microevolution and phylogeography. With dates a century wide, two strains found in different towns can look contemporary when they are not. The press release notes that Yersinia pestis still survives in wild rodents in several regions of the world.

The main limitations are already in the abstract. The links to epidemics are tentative. Fifteen of the twenty-six new genomes are low coverage. Full methods, funding, competing interests and any statement on the use of artificial intelligence are in the full text, which was not read. An earlier version of the work appeared as a preprint, not yet reviewed by other experts, in July 2023.
Radiocarbon says there was plague in that grave. The bacterium’s family tree, set beside it, helps say which one.

References
Keller M., Guellil M., Slavin P. et al., Tambets K., Scheib C.L., «A refined phylochronology of the second plague pandemic in Western Eurasia», Proceedings of the National Academy of Sciences of the United States of America, 123, 37, e2534899123, 10 September 2026, open access under CC BY-NC-ND. doi: 10.1073/pnas.2534899123
Keller M. et al., «A Refined Phylochronology of the Second Plague Pandemic in Western Eurasia», bioRxiv preprint, July 2023. doi: 10.1101/2023.07.18.549544
Estonian Research Council, press release, republished by ScienceDaily on 20 September 2026 as «Ancient DNA Reveals How Plague Kept Returning for 400 Years After the Black Death».