This is not correct. Not only was it imaginable... it was widely predicted in March that COVID would be a highly persistent problem.

1. An expert panel in March predicted ~200K US deaths this year:

https://fivethirtyeight.com/features/infectious-disease-experts-dont-know-how-bad-the-coronavirus-is-going-to-get-either/ https://twitter.com/JustinWolfers/status/1296062969227378690

2. The Imperial College study in March envisioned on-and-off waves of COVID until a vaccine, if social distancing measures were implemented then relaxed then re-implemented, etc. (which is basically what has happened).

https://www.imperial.ac.uk/media/imperial-college/medicine/sph/ide/gida-fellowships/Imperial-College-COVID19-NPI-modelling-16-03-2020.pdf

3. Prominent epidemiologists like Marc Lipsitch predicted in February that 40-70% of the world's population would be infected with COVID-19 over the next year. https://www.theatlantic.com/health/archive/2020/02/covid-vaccine/607000/

So if forecasts were pretty good in March, what changed?

Part of it is was just this was very new in March. People weren't thinking so far ahead. Fall seemed a LONG time away. You could read these predictions, agree with them intellectually, but they didn't register emotionally.

But also, we wound up in a middle ground where given the sort of interventions that society is willing to undertake, R seems to hover around 1. Achieving true suppression (R << 1) is too hard, apparently*. But it's not that hard to prevent R >> 1 with moderate interventions**.

** If it had been impossible to keep R from falling to <1, COVID would run its course until herd immunity. Indeed this is what some March predictions assumed. This would have been VERY bad. But it does mean it might have been "over" at some point, depending on length of immunity.

* People hate when this is brought up, but part of the problem with suppression via lockdowns is that unless you either achieve eradication (~impossible) or use the time under lockdowns to improve technology (e.g. testing) cases start rising again once you relax the measures.

I'm not sure elite discourse around lockdowns in March was especially honest with itself about this, especially the likelihood of achieving technological improvements (such as fast-turnaround testing) on a short time frame in countries with poor governance (including the US).