Currently, there are no studies as to how long immunity lasts for patients who have had Covid 19 and then tested negative after a course of treatment, or after a 14 day quarantine. In fact, there is some concern of repeat episodes of Covid 19 in those who have had the illness. Many who have tested negative for Covid 19 after having had it, still have ongoing debilitating symptoms and heart and lung damage that may or may not get better. These are called "long haulers." There are articles on this subject.Also, immunity from a vaccine is supposed to be much stronger than immunity from simply contracting Covid itself.
These folks are frustrated and angry because of their doctors telling them it's all from stress or depression.
An effective vaccine certainly has the potential to immunize those taking it, at least to a fair degree of reliability.
Yes, the polio vaccine did work.