Yes, said that decades ago when schools put in a/c and did away with windows that opened. Right there is why we have such a problem with the regular flu. These days, schools close left and right for flu season but we never had that problem back in the ‘70s.
Around here the cause of schools closing is almost always because on an outbreak of norovirus. Which is disgusting enough.
The elementary school I attended in the 60s used to have an entire wall of windows you could open in each classroom. About 20 years ago the district bricked them up, leaving only a single window in each classroom. I always wondered about the lack of air circulation, especially not getting fresh air.