They never said 100% effective. No vaccine is.
Reduce hospitalization, yes, reduce death, yes.
That much has been accomplished.
Understanding evolution and how often small things like viruses and bacteria mutate, you might realize that methicillin resistant staph (Penicillin resistant) and methicillin pneumonia, evolved because of routine use of antibiotics in the food supply and in medicine.
Same with viruses, about every two weeks viruses mutate in many different directions. Some are unsuccessful, some or often one is most successful at being more contagious, but less deadly. This is a natural process, just like flu, and other viruses and bacteria.
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