The smallpox epidemic that would spread over most of North America and last throughout the Revolutionary War first appeared in Boston in 1774 and festered during the long siege of the British-occupied town, April 1775-March 1776. While smallpox inoculation--the insertion of live smallpox virus under the skin--had been widely known and practiced in Boston for more than fifty years, it remained controversial and dangerous. The Revolutionary government of Massachusetts forbade inoculation in favor of a strict quarantine, but lifted the ban a few days before news of the Declaration of Independence reached Boston. Unfortunately, the disease remained poorly understood and as Henry Alline's references to making his children "keep about, as the Doctrs. say it is necessary" indicate, people who had been inoculated moved about freely while they still were contagious. Abigail Adams, who, along with her children, had been recently inoculated in Boston also was in the crowd that witnessed the proclamation of Independence on 18 July; see the online presentation of the letter from Abigail Adams to John Adams, 21 July 1776.

In addition to the accounts of Henry Alline and Abigail Adams, the Historical Society holds a third, less-detailed diary account of the proclamation of Independence in Boston by merchant John Rowe; see the online presentation of the diary entry by Rowe, dating from 18 July 1776. The Historical Society purchased the Henry Alline letter in 1987. As it is not part of a collection of personal or family papers, the Society has less information about Alline and his family than for other items in the MHS manuscript collection, but Alline lived on in Boston until his death in 1804, and three generations of his family served as registers of deeds for Suffolk County, Massachusetts.