When you search that date, you will find that that is the date in 1776, that Boston closed the guardhouses and opened back up. It was called "Freedom Summer" Inoculation against smallpox worked:
https://www.washingtonpost.com/outlook/ ... om-summer/
The same day, a letter in the New England Chronicle signed “A.B.” praised inoculation by writing, “At this critical season, we cannot be too speedy or diligent in everywhere applying this inestimable gift of Heaven.” A.B. claimed that by providing inoculation to the public, the government “cannot in any way more essentially serve this Colony, and the common cause of America,” and implored “all friends to their country to contribute their aid to a service of so much importance.”
Boston’s “freedom summer” ended on Sept. 18, 1776, when the city ordered the guardhouses closed and the city to reopen for business. Although statistics were not immediately published, 20 years later, Thomas Pemberton, a businessman and member of the newly founded Massachusetts Historical Society, compiled the numbers. In the summer of 1776, Boston saw 29 deaths from 304 cases of natural smallpox. By contrast, only 28 deaths were reported with 4,988 Bostonians inoculated. Ninety percent of Boston’s nonimmune population was inoculated, saving hundreds of lives.