California Code, Health and Safety Code - HSC § 120370

(a)(1) Prior to January 1, 2021, if the parent or guardian files with the governing authority a written statement by a licensed physician and surgeon to the effect that the physical condition of the child is such, or medical circumstances relating to the child are such, that immunization is not considered safe, indicating the specific nature and probable duration of the medical condition or circumstances, including, but not limited to, family medical history, for which the physician and surgeon does not recommend immunization, that child shall be exempt from the requirements of this chapter, except for Section 120380, and exempt from Sections 120400, 120405, 120410, and 120415 to the extent indicated by the physician and surgeon's statement.

(2) Commencing January 1, 2020, a child who has a medical exemption issued before January 1, 2020, shall be allowed continued enrollment to any public or private elementary or secondary school, child care center, day nursery, nursery school, family day care home, or developmental center within the state until the child enrolls in the next grade span.

For purposes of this subdivision, “grade span” means each of the following:

(3) Except as provided in this subdivision, on and after July 1, 2021, the governing authority shall not unconditionally admit or readmit to any of those institutions specified in this subdivision, or admit or advance any pupil to 7th grade level, unless the pupil has been immunized pursuant to Section 120335 or the parent or guardian files a medical exemption form that complies with Section 120372.