I don't see how anyone could not have seen this path coming.
“If you choose to continue to wear a mask once vaccinated, that’s on YOU, not the other people.”
The mRNA vaccines are coated. It takes time (about 7 to 10 days) for the vaccine to get out and become effective.
In the elderly, about 5 to 10% of those vaccinated against Covid with Western Covid vaccines will not develop strong immunity. If you are an adult and normally prone to get sick, be careful in your lifestyle until Covid antibody testing becomes common and you know you have effective antibodies to Covid.