Context: In 2012, California instituted a new requirement for parents to consult with a clinician before receiving a personal belief exemption to its school entry vaccine mandate. In 2015, the state removed this exemption altogether. In 2019, legislators cracked down on medical exemptions to address their misuse by vaccine refusers and supportive clinicians. This paper explores these political conflicts using ‘policy feedback theory,’ arguing that personal belief exemptions informed the emergence and approaches of two coalitions whose conflict reshaped California's vaccination policies.

Methods: We analysed legal, policy, academic and media documents; interviewed ten key informants; and deductively analysed transcripts using NVivo 20 transcription software.

Findings: California's long-standing vaccination policy inadvertently disseminated two fundamentally incompatible social norms: vaccination is a choice; vaccination is not a choice. Over time, the culture and number of vaccine refusers grew, at least in part because the policy state-sanctioned the norm of vaccine refusal.

Conclusions: The long-term consequences of California's ‘mandate + PBE’ policy – visible, public, and socially sanctioned vaccine refusal – undermined support for it over time, generating well-defined losses for a large group of people (the vaccinating public) and specifically for the parent activists whose experiences of personal grievance drove their mobilisation for change.

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Supplementary data