EDIT: I've missed that personal belief exemption is no longer allowed. Anyway, what's below shows that it WAS an issue, and quite recently. Also while kids should be vaccinated now due to the law it still tells something about ideas parents hold.

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"We require parents to follow all state laws regarding immunization" actually allows "personal belief exemptions", since it is a part of laws.

And few links from few years ago:

SF: https://www.sfwaldorf.org/uploaded/docs/gs/gs_health_and_ill...

Also "On the other side of the bay, about two-thirds of the students at the private Waldorf School in upscale Los Altos Hills didn’t have the proper immunizations." - https://www.mercurynews.com/2015/01/26/measles-outbreak-low-...

In general official Waldorf policy is that there is no policy