Phase three clinical trials for the Pfizer vaccine ran ~16 weeks.
You need a minimum of 5 weeks before you can begin your challenge trials, starting from the same point, for the 3 weeks between doses and the 2 weeks after the second dose where immunity is being tested.
If you run three 2-week rounds of challenge trials after that, you're already up to 11 weeks to finish your challenge trials and begin administering the vaccines to the population at large, versus the 16 weeks for a regular-old phase 3 trial.
Now, five weeks is nothing to sneeze at -- given the other parameters, it's not unreasonable to think that on the order of a thousand deaths could have been prevented by using what vaccine supply we had available earlier -- but it's also patently not the case that we would be five weeks ahead of where we are now if we had started vaccinating earlier: we spent most of the last five months in the US supply constrained, and we didn't wait to start building out our capacity, so we'd probably be at the same point we are now in terms of total vaccinated today regardless of whether we started vaccinating 5 weeks earlier or 5 weeks later.
You need a minimum of 5 weeks before you can begin your challenge trials, starting from the same point, for the 3 weeks between doses and the 2 weeks after the second dose where immunity is being tested.
If you run three 2-week rounds of challenge trials after that, you're already up to 11 weeks to finish your challenge trials and begin administering the vaccines to the population at large, versus the 16 weeks for a regular-old phase 3 trial.
Now, five weeks is nothing to sneeze at -- given the other parameters, it's not unreasonable to think that on the order of a thousand deaths could have been prevented by using what vaccine supply we had available earlier -- but it's also patently not the case that we would be five weeks ahead of where we are now if we had started vaccinating earlier: we spent most of the last five months in the US supply constrained, and we didn't wait to start building out our capacity, so we'd probably be at the same point we are now in terms of total vaccinated today regardless of whether we started vaccinating 5 weeks earlier or 5 weeks later.