An internal FDA memo from CBER director Vinay Prasad proposing sweeping changes to vaccine approval and authoring processes became public, prompting immediate sector reaction and stock moves. The memo calls for more randomized evidence for vaccines across populations and questions extrapolations used during the pandemic. Vaccine developers’ shares dipped as investors parsed the memo’s potential to raise regulatory demands, increase evidentiary burden and slow modifications to existing vaccines. Industry groups and some clinical experts signaled concerns that new requirements could increase costs and delay access. Regulatory advisors and policy makers now face a choice between stronger safety evidence and potential delays to vaccine availability; companies are reassessing development plans and messaging ahead of advisory committee meetings.