Your readers may be interested in this article that supports very much the get enough sleep theory to reduce the chance of catching a cold/flu:
http://www.nhs.uk/news/2015/09September/Pages/does-lack-of-sleep-make-you-susceptible-to-common-cold.aspx

I would also add to your advice that if a student or member of staff is feeling ill or showing the first signs of a cold or flu, please stay at home and keep the bugs away. Probably a doctor could define “first signs” better!