"For now, the industry says it has plenty of horseshoe crab blood to screen coronavirus vaccines. Pharmaceutical companies test a sample from a batch of vaccines, not every dose. And that sample size, say three vials, doesn’t change whether the batch contains 100,000 doses or 1 million, says Allen Burgenson of Lonza.

In fact, Burgenson says, the industry produces enough tests in one day to screen 5 billion doses of coronavirus vaccine."

(I think this is unduly optimistic, because mfrs are likely to screen at multiple steps during production, since the latency of batches is ~100 days, and because lot sizes aren't so large yet. So divide 5 billion by a small integer).