My child is 17 and working full time now, no longer in school but of course I hope (not too soon) that I'll have grandchildren. I have a niece and nephews still in school though.
My idea (which has been implemented by govts in some countries) is not 'dumb' it's not even my idea!
Germany are bringing into law a system of fining parents who don't vaccinate as response to a rise in measles cases.
I don't have blind faith in vaccines.
I have educated faith that they do what is claimed and massively REDUCE the risk of both getting those infections and if my child did, how seriously she would be affected.
I have educated faith that good hygiene, nutrition, and when necessary treatment of wounds and disease ALSO protects my dd and reduces her risk of getting certain infections.
I have educated faith in the facts around herd immunity and am angry others don't take responsibility in providing it while happy to benefit from it (like op's sil).
I have at the age of 46 seen first hand the effects of certain diseases inc in the immunocompromised both as a relative and as a nurse. Unfortunately not everyone can be vaccinated but yes! Based on my experience, training and knowledge I strongly believe those who can should be.
My dd has a disability which means that if she were to contract certain diseases she would almost certainly be hospitalised, if not worse.
In fact a couple Christmases ago she contracted a condition which for most people can be treated easily with otc meds and wouldn't even need them to stay off school/work. But for the immunocompromised and those with certain other conditions can be extremely dangerous. I believe they're working on a vaccine for it.
For my dd it meant a 3 week stay in hospital, on iv meds, enteral feeding for the first ten days, then liquids only until the last couple days when she could finally manage soft foods. Soft foods continued at home while she gradually got used to more substantial food.
She's a very slim child always has been (all my family are until we have kids - in the case of the women) and lost a lot of weight she really couldn't afford to. Struggled walking to the loo, needed to use a chair in the shower while in hospital and when we got home had baths initially that I helped her in and out of.
This was a normally fairly fit and healthy 15 yr old at the time.
Her disability is largely invisible to others but she feels it daily, because the main symptom is pain.
I was extremely worried at the time (a lovely mner chatted away to me while I watched over her fretting and feeling utterly powerless).
I dread to think what would have happened to her if we didn't live in a country where vaccinations are not only easily accessible and reliable but free. I suspect I'd have lost her a long time ago.