As an ex fund manager, albeit with little macro experience, here's some thoughts.
The time since the GFC is a sort of strange era. Again and again, we're told that central banks (and governments) are going to do whatever the heck keeps the market up. Buying the dip has more or less worked the whole time. A lot of asset classes look expensive if you take a longer-back view of things, but then again that longer view tended to not include "we'll do anything".
This virus thing could be quite a different thing to what traders and fund managers are used to. The kinds of things I used to look at were things like what do the brokers say about rates, or what do economists think about oil. Or more specifially for me what does the market think about the supply and demand of volatility risk. Even the GFC itself was something that many people in my circles had thought about. It was definitely in the financial arena; either you thought subprime was gonna be a mess, or you thought it would stay localized and not burst its banks.
Also keep in mind traders tend to be young, and there has been a trend towards juniorization particularly in the investment banks.
I'm in the UK at the moment, and the number of cases doubled in the last couple of days. It did the same a couple of days earlier. So then the question is whether this is an exponential process. And if it is, what's going to stop it being exponential? Public awareness isn't going to be it, because everyone in the whole world already knows they're supposed to wash their hands and stay away from old people.
Certainly we can't just pretend the virus is not here. An expert on the radio last night mentioned that if Twickenham was full for the match today, and the 80k people there all had flu, 8 of them would be expected to die. According to him with Coronavirus at 2-3% it would be in the ballpark of 2000. Chances are people who would be ill but recover would also be a fair chunk.
So something has to be done, governments aren't going to get away with just playing it down as the numbers double every other day.
And this is where fragility comes into play. We're used to the economy being coated in a thick layer of cheap money. Business models that were previously tenuous now seem solid, because there's always someone who will finance it. I'm sure you've heard of a few such businesses in the recent news. What this translates into is that you can motivate people to work in a certain way because you can borrow (and this is in the larger sense, not just loans) the firepower to pay them.
But what if a bunch of people suddenly cannot work? If you're properly ill, there's no amount of money that will make you able to work. And you will have to live with not earning money, and your boss will have to live with work not getting done. It doesn't seem like something that handing more money out for will help. At most you can help to make sure that peripheral issues are solved, like cash crises in people's private finances don't cause them to have to sell their house or business. But people not being able to work on a large scale will cause some kind of collapse somewhere in the system, and supply and demand isn't going to generate more supply, it will just raise the price of work. This is kinda like how historians write that peasants had a great time after the plague killed a third of Europe.
And of course companies are negotiating with labor over the spoils of production, so profits would seem to go down.
But this is all pretty sensitive to the size of the actual outbreak. If the top is today the death toll is similar to 9/11, and the economy will be fine. If it grows to shut down schools and workplaces all over the world, it's gonna be really interesting.