D3 said..
None, because the systems (as crude as they are) are working to keep the infection rate down.
Check in with anyone you know in Indonesia and the UK in about 3 weeks time to see what almost uncontrolled spread looks like.
Daily cases started spiking two months ago -- death rate hasn't matched it.
(And of course the test is very sensitive. It's like a breathalyzer that can detect the alcohol from the rum & raisin chocolate the night before, but you're in no way physically impaired. Positive = going to die.)
Could be a reason why:

The vaccine is to stop you getting a severe illness or dying, its goal is not -- unlike the Australian premiers LOL -- to grant you complete and total immunity in order to stop people getting sick even a little.
... and now, cue the self-appointed gatekeeper of all knowledge and sources of authority