Nothing about the virus is going to be 100% effective. It's a matter of compositing things that are 60% effective and 90% effective and 50% effective.
If they require testing which is 80% effective, and masks which are 80% effective, and get vaccination up to xx%... etc etc. You eliminate vectors for the virus one at a time and eventually there aren't enough vulnerable people contacting each other in ways that are contagious.
If they require testing which is 80% effective, and masks which are 80% effective, and get vaccination up to xx%... etc etc. You eliminate vectors for the virus one at a time and eventually there aren't enough vulnerable people contacting each other in ways that are contagious.
(Percentages are guesses)