https://astralcodexten.substack.com/p/highlights-from-the-comments-on-the

Andrew writes:

One word I don't see mentioned anywhere is "manufacturing." It's one thing to make enough drug for a clinical trial, it's another to make millions of commercial doses reliably. FDA approval requires inspection of and confidence in these commercial-scale manufacturing processes.

Zutano adds:

To expand on this more: the clinical trials only show that *that one particular batch* was safe and efficacious (the FDA thinks this, since they agreed to terminate the trial early). Pfizer must then show that the commercial batches will be identical in every relevant way to the clinical trial batches, so that they will have the same safety and efficacy. What are the relevant ways? Pfizer must decide that, and justify their decisions to the FDA with supporting evidence.

Scaling up chemical manufacturing is not trivial (a regular contender for Understatement of the Year). E.g. heating and stirring work differently in different sized reactors. Heat transfer in and out of your reactor works through surface area, but heat produced/consumed by the reaction depends on volume. If your stirrer design isn't right for the viscosity of the solution, you might get hotspots and so on.

Ideally, the FDA expects you to understand the chemistry so thoroughly that you know everything that can possibly go wrong, and design your commercial process so that none of these things can possibly happen. The commercial batches will therefore be identical *by design* to the clinical trial batches, and you have to prove this with science.