During the Great Northern War (1700–1721), many towns and areas around the Baltic Sea and East-Central Europe had a severe outbreak of the plague with a peak from 1708 to 1712. This epidemic was probably part of a pandemic affecting an area from Central Asia to the Mediterranean. Most probably via Constantinople, it spread to Pińczów in southern Poland, where it was first recorded in a Swedish military hospital in 1702. The plague then followed trade, travel and army routes, reached the Baltic coast at Prussia in 1709, affected areas all around the Baltic Sea by 1711 and reached Hamburg by 1712. Therefore, the course of the war and the course of the plague mutually affected each other: while soldiers and refugees were often agents of the plague, the death toll in the military as well as the depopulation of towns and rural areas sometimes severely impacted the ability to resist enemy forces or to supply troops.
This plague was the last to affect the area around the Baltic, which had experienced several waves of the plague since the Black Death of the 14th century. However, for some areas, it was the most severe. People died within a few days of first showing symptoms. Especially on the eastern coast from Prussia to Estonia, the average death toll for wide areas was up to two thirds or three quarters of the population, and many farms and villages were left completely desolated. It is, however, hard to distinguish between deaths due to a genuine plague infection and deaths due to starvation and other diseases that spread along with the plague. While buboes are recorded among the symptoms, contemporary means of diagnosis were poorly developed, and death records are often unspecific, incomplete or lost. Some towns and areas were affected only for one year, while in other places the plague recurred annually throughout several subsequent years. In some areas, a disproportionally high death toll is recorded for children and women, which may be due to famine and the men being drafted.
As the cause of the plague was unknown to contemporaries, with speculations reaching from religious causes over "bad air" to contaminated clothes, the only means of fighting the disease was containment, to separate the ill from the healthy. Cordons sanitaire were established around infected towns like Stralsund and Königsberg; one was also established around the whole Duchy of Prussia and another one between Scania and the Danish isles along the Sound, with Saltholm as the central quarantine station. "Plague houses" to quarantine infected people were established within or before the city walls. An example of the latter is the Charité of Berlin, which was spared from the plague.
Background
Local outbreaks of the plague are grouped into three plague pandemics, whereby the respective start and end dates and the assignment of some outbreaks to one or another pandemic are still subject to discussion. According to Joseph P. Byrne from Belmont University, the pandemics were:
the first plague pandemic from 541 to ~750, spreading from Egypt to the Mediterranean (starting with the Plague of Justinian) and northwestern Europe the second plague pandemic from ~1345 to ~1840, spreading from Central Asia to the Mediterranean and Europe (starting with the Black Death), and probably also to China the third plague pandemic from 1866 to the 1960s, spreading from China to various places around the world, notably the US-American west coast and India. However, the late medieval Black Death is sometimes seen not as the start of the second, but as the end of the first pandemic – in that case, the second pandemic's start would be 1361; the end dates of the second pandemic given in literature also vary, e.g. ~1890 instead of ~1840.
The plague during the Great Northern War falls within the second pandemic, which by the late 17th century had its final recurrence in western Europe (e.g. the Great Plague of London 1666–68) and, in the 18th century final recurrences in the rest of Europe (e.g. the plague during the Great Northern War in the area around the Baltic sea, the Great Plague of Marseille 1720–22 in southern Europe, and the Russian plague of 1770–1772 in eastern Europe), being thereafter confined to less severe outbreaks in ports of the Ottoman Empire until the 1830s.