Apparently, the possible need for additional boosters during the 22/23 year had been repeatedly mentioned throughout the spring and then had been explicitly restated as late as July 27:
“As of September 1, students, faculty, and staff are required to be fully up-to-date, as defined by the U.S. Centers for Disease Control and Prevention (CDC).”
The referenced CDC definition of “up to date” is:
When Are You Up to Date?
You are up to date with your COVID-19 vaccines if you have completed a COVID-19 vaccine primary series and received the most recent booster dose recommended for you by CDC.
So maybe their policy requiring to be up to date with the most-current, recommended booster had always been in place, just that some people weren’t that focused on campus policies, when the news around the city itself had focused on lifting restrictions.
And, of course, many parents could have understood the policy all along, never finding it the least controversial.