Although I HAVE heard a few references to 'RULES' most of what I read is still couched in terms of GUIDANCE and ADVICE, which overall gives a relaxed and optional feel to things instead of emphasing that theses are COMPULSARY instructions that MUST be adhered to.
Also the language used when Talking about the risk people face suggests it is the risk of CATCHING the virus that varies in these various population groups. whereas the risk of catching it is the same for everyone and it is the risk of severity of its EFFECT that varies!