There is a great book called "Dissolving Illusions" that goes into great detail on polio vax, and others. Very well cited. If you can find the polio chapter online, it is worth a read. To end the pandemic, health authorities changed the definition of polio. I think with COVID, when health authorities are ready to end the pandemic, they will switch to less sensitive tests and poof, this pandemic will be over and the vaccine will get the credit.