Where Covid vaccination could work (remains to be seen) is if, combined with other mitigation measures, it brings the effective reproduction rate down low enough and for long enough to eradicate the virus. Problem is, the long tail can last for years, and every time the goal has been within grasp, people would see the falling numbers and assume that meant it was already over. Vaccination makes that less of a problem.
Polio and MMR vaccines aren't 99.9999% effective, either. More like 80-99%. A breakthrough is extremely unlikely because you're not likely to be exposed to those viruses at all anymore. But it took decades to reach this point.
Polio and MMR vaccines aren't 99.9999% effective, either. More like 80-99%. A breakthrough is extremely unlikely because you're not likely to be exposed to those viruses at all anymore. But it took decades to reach this point.