I'm puzzled by the response to the fact that Moderna had its vaccine candidate ready just days after the coronavirus sequence was known. "It took just *two days*?!! So we've had the vaccine all this time?" First, this is the whole point of mNRA vaccines... (1/n)

All you need is the sequence of the target protein, and you can almost instantly make a candidate vaccine. (Of course, you need to know the target; in this case we had experience with SARS and MERS to draw on.) (2/n)

This is one of the advantages of the mRNA approach - the active ingredient is quick and easy to make by chemical means. It's what should make mRNA such a good (though not the only) vaccine platform technology in the future. BUT... (3/n)

What Moderna had was not the vaccine but a vaccine candidate. It's not clear how any of the trials could have been omitted or, perhaps, significantly shortened or speeded up. Even if you know the vaccine is basically safe (after Phase I), who on earth is going to risk...

...plunging into large-scale manufacture and distribution for a vaccine candidate that might not work (even if you expect it will?). That would be an immense diversion of resources and money. (As it stood, manufacture *was* begun at an early stage, thanks to...

... Operation Warp Speed funding - but it would have been crazy to do that at scale *too* early.) What would be lost if it hadn't worked? Loads. Vaccinated people could have had a false sense of security, and a vaccine that proved not effective enough could have...

...shattered (already fragile) public trust. Plus, mRNA vaccines have never been approved before, so there's no way the trials could be skimped at this point. As for whether, now that we know it works, we could demand less of efficacy (not safety!) trials in future...

... efficacy for one virus does not guarantee it for another. SARS-CoV-2 is in many ways a soft target, with few apparent evasion mechanisms. Other families of viruses can be better at evading an immune response. So it's not a given.