If producing a vaccine that quickly was something we can just routinely do, then why don't we do it all the time?
It's not routine at all.
That's like asking if Usain Bolt can run a 100m race in 10 seconds, why can't he run a 400m race in 40 seconds and a 5K in 500 seconds?
The FDA has a LOT going on at any given point. They have a queue of a ton of different medicines, vaccines, etc under review all the time. There's various bureaucracy and check points in the process, things have to wait their turn, and all in all it can take a while.
For this, my understanding is that no "corners were cut" regarding safety protocols and testing. What sped it through so quickly is that ALL of the queuing and process delays which would normally be there is what was cut. It got put as priority #1 on the FDA review list, ahead of anything else in the queue.
That's how it got through so quickly. It got pushed to the front of the line ahead of anything else, which is only done in extreme circumstances (such as a worldwide pandemic that has killed >450K Americans).
BTW on top of that, one of the advantages of this type of vaccine is that the mRNA concept by itself carries certain lower risks than other vaccines. Traditional vaccines often use attenuated or dead virus cells, and those cells often need to be grown in a lab. This carries a risk because there's a chance you can actually contract the disease from the vaccine if something goes wrong--that's impossible with this design. In addition, it doesn't need to be "grown" in living cells, so there's another benefit for production. That's why they said that they had the vaccine produced for testing within something like a week to a month from having the virus DNA sequenced.
So we can't just "routinely" do something like this...
