Yes, patients can sue if the pharmacist makes a mistake. This would be true with any concoction that is prepared by the pharmacist and dispensed incorrectly. The pharmacy, Wal-Greens, in this case is responsible for contacting the patient(s) once the error is determined and they do a lot of damage control. If the mistake is fatal, well then they are in a shit-ton of trouble. Malpractice insurance is a must for pharmacists and doctors.

Note; my daughter and SIL are both pharmacists and have been mixing and administering the vax for patients for a few months now.