“In this year, the sun was eclipsed on the 5th before the Nones of May [that is, May 1]…the same year, there was great pestilence in the island Britain.” – The Anglo-Saxon Chronicle, 664
“A great mortality in Ireland came on the kalends of August [August 1]” – The Annals of Tignerach, 664
The year 664 was a sorrowful one for the inhabitants of Britain and Ireland. Both churchmen and laity interpreted the partial eclipse on May 1 as a bad omen heralding the deadly epidemic later that summer. Both spring and summer were exceptionally warm that year, with warm weather stretching late into autumn, perfect for spreading disease. The outbreak first occurred among the Anglo-Saxons in the south of England, although this was before “England” existed. It spread north to the kingdom of Northumbria (today Yorkshire), west into Wales, and thence across the Irish Sea to Ireland. The Irish called it “Stubble-Yellow Plague”, named after the color of grain stubble in harvested fields, because of the jaundiced appearance of the sick. Historians of subsequent centuries have called it smallpox.
Even in 664, writers noticed that the virus was spread by “the air.” One Welsh source described the disease as a veil of rain sweeping through the countryside. Close contact with infected people was understood to lead to new infections, even though the science of “droplets” wasn’t yet formed.
Most of our information about the Yellow Plague comes from the Venerable Bede, a monk from Northumbria who wrote a sweeping history of the English church a generation after the epidemic. He noted the deaths of important Anglo-Saxon monks and clergy, many of whom had gone to Ireland to receive a quality religious education. Unfortunately, the movement of monks between monasteries both in Ireland and back in Great Britain helped to spread smallpox to more people. The following passage on the outbreak is from his Ecclesiastical History. His first sentence is taken verbatim from the Anglo-Saxon Chronicle.

“In the same year of our Lord 664, there happened an eclipse of the sun, on the…[first] day of May…In the same year, a sudden pestilence depopulated first the southern parts of Britain, and afterwards attacking the province of the Northumbrians, ravaged the country far and near, and destroyed a great multitude of men…Moreover, this plague prevailed no less disastrously in the island of Ireland. Many of the nobility, and of the lower ranks of the English nation, were there at that time, who, in the days of the Bishops Finan and Colman, forsaking their native island, retired thither, either for the sake of sacred studies, or of a more ascetic life; and some of them presently devoted themselves faithfully to a monastic life, others chose rather to apply themselves to study, going about from one master’s cell to another. The [Irish] willingly received them all, and took care to supply them with daily food without cost, as also to furnish them with books for their studies, and teaching free of charge.
Among these were Ethelhun and Egbert, two youths of great capacity, of the English nobility…These two being in the monastery which in the language of the [Irish] is called Rath Melsigi, and having lost all their companions, who were either cut off by the plague, or dispersed into other places, were both seized by the same sickness, and grievously afflicted. Of these, Egbert…concluding that he was at the point of death, went out of the chamber, where the sick lay…and sitting alone in a fitting place, began seriously to reflect upon his past actions, and, being full of compunction at the remembrance of his sins, bedewed his face with tears, and prayed fervently to God that he might not die yet, before he could forthwith more fully make amends for the careless offences which he had committed in his boyhood and infancy, or might further exercise himself in good works. He also made a vow that he would spend all his life abroad and never return into the island of Britain, where he was born; that besides singing the psalms at the canonical hours, he would, unless prevented by bodily infirmity, repeat the whole Psalter daily to the praise of God; and that he would every week fast one whole day and night. Returning home, after his tears and prayers and vows, he found his companion asleep; and going to bed himself, he began to compose himself to rest. When he had lain quiet awhile, his comrade awaking, looked on him, and said, “Alas! Brother Egbert, what have you done? I was in hopes that we should have entered together into life everlasting; but know that your prayer is granted.” For he had learned in a vision what the other had requested, and that he had obtained his request.

In brief, Ethelhun died the next night; but Egbert, throwing off his sickness, recovered and lived a long time after to grace the episcopal office, which he received by deeds worthy of it; and blessed with many virtues, according to his desire…[I]n the year of our Lord 729, being ninety years of age, he departed to the heavenly kingdom. He passed his life in great perfection of humility, gentleness, continence, simplicity, and justice. Thus he was a great benefactor, both to his own people, and to those nations of the Scots and Picts among whom he lived in exile, by the example of his life, his earnestness in teaching, his authority in reproving, and his piety in giving away of those things which he received from the rich. …
At the same time [in 665], the Kings Sighere and Sebbi, though themselves subject to Wulfhere, king of the Mercians, governed the province of the East Saxons after Suidhelm, of whom we have spoken above. When that province was suffering from the aforesaid disastrous plague, Sighere, with his part of the people, forsook the mysteries of the Christian Faith, and turned apostate. For the king himself, and many of the commons and nobles, loving this life, and not seeking after another, or even not believing in any other, began to restore the temples that had been abandoned, and to adore idols, as if they might by those means be protected against the plague. But Sebbi, his companion and co-heir in the kingdom, with all his people, very devoutly preserved the Faith which he had received, and, as we shall show hereafter, ended his faithful life in great felicity.
King Wulfhere, hearing that the faith of the province was in part profaned, sent Bishop Jaruman, who was successor to Trumhere, to correct their error, and recall the province to the true Faith. He acted with much discretion, as I was informed by a priest who bore him company in that journey, and had been his fellow labourer in the Word, for he was a religious and good man, and travelling through all the country, far and near, brought back both the people and the aforesaid king to the way of righteousness, so that, either forsaking or destroying the temples and altars which they had erected, they opened the churches, and gladly confessed the Name of Christ, which they had opposed, choosing rather to die in the faith of resurrection in Him, than to live in the abominations of unbelief among their idols. Having thus accomplished their works, the priests and teachers returned home with joy.”
Bede, Ecclesiastical History of the English People, Book 3, chs. 27 and 30.