That's because those vaccines were stored in the freezer longer than the manufacturer recommends, county health officials said in a news release Wednesday.
Riverside University Health System says 324 people received the doses at sites in Riverside and Jurupa Valley.
The specific locations of those sites are Riverside Neighborhood Clinic at 7140 Indiana Avenue and Jurupa Valley (CHC) at 8876 Mission Blvd.
The doses were administered Oct. 8 - Nov. 23 at the site in Jurupa Valley and Oct. 23 - Nov. 23 at the Riverside site.
The vaccines do not pose a danger, but they may have lost their potency after being stored for so long.
Patients who received a Pfizer vaccine at the Jurupa Valley or Riverside sites during those specific days and who have not been contacted by the county by Thursday can call 800-945-6171 between 8:30 a.m. and 5 p.m. on weekdays.
For those who received those vaccines, the Centers for Disease Control and Prevention is recommending a repeat dose as soon as possible.