I recently asked on Twitter:
And got reassuring results:
Then I asked another question. Have a think about how you might answer it.
Here is how Twitter responded:
Quite a difference!
Until recently, the strategy for COVID testing in many countries has been focused on people who have a significantly likelihood of having COVID-19. The need to impose unpleasant social distancing measures, and ultimately complete lock-downs, trades off against how much testing you do in the community.
Update: it seems (although clarity is lacking) that the UK has moved away from the herd-immunity strategy. I very much welcome this. It renders the argument below irrelevant, except as an illustration of the weaknesses of a strategy that seeks to vaccinate a population using an epidemic.