Under the safe-harbor deidentification guide you posted, all dates must be removed except for the year. If this was done on a clinical trial dataset, the data would be useless. Specifically for the COVID vaccine trial, the “statistic” used is the number of days between when the patient enters the study and when they get COVID. This is called TTE or time-to-event and underpins the entire study design. You need the exact date the patient entered the study AND contracted COVID to calculate the TTE value. Without this information, you have no chance of validating the results of the study.