It takes time for immunity to develop from vaccines - it is not overnight. The testing standard for the Phizer Vaccine was at 28 days after the first shot (7 days after the second). Very elderly, frail patients might be slower to achieve that level of immunity.
It sounds like unfortunate timing, that the outbreak occurred before immunity had developed from the vaccine.
If only they had not delayed approval until after the election...
“It sounds like unfortunate timing, that the outbreak occurred before immunity had developed from the vaccine.”
The outbreak started one day BEFORE the first vaccination.