Not sure what the *exact* timings/etc. are of this, but according to the article, it's got a case study by the CDC (trying to find the actual study).
Basically the news article says a teacher removed her mask briefly and infected half her class with COVID.
Article actually written/whatever by Ariana Eunjung Cha, The Washington Post on 8/28/21 it seems.

https://www.timesunion.com/news/arti...-Editors-Picks