Everyone's forgotten by now but back when schools were trying to open up again it was very common for them to be closed again a week or two later because whoops looks like half the staff are out sick and we literally don't have enough people to run the place!
Also cancellations or 'so we're not actually getting ahead in the curriculum today' situations because there just weren't enough kids. Ever since swine flu, the schools where my parents live close for disinfection and transmission breaking if enough kids are already out with the same illness.