The Palo Alto Medical Foundation is warning parents that their children may need to repeat their vaccinations.
A bad refrigerator inside the foundation's Los Gatos office had been keeping vaccines a couple degrees too cold, possibly ruining the vaccines.
The vaccines in question were administered from February 2014 through March 2015. More than 4,000 pediatric patients were notified of the possible issue with vaccinations.
Experts said the vaccines are safe, but because they were stored a bit too cold they could be less effective.
"There is nothing unsafe about any vaccines," said Dr. David Quinn of the Palo Alto Medical Foundation. "The only question is -- is it as effective as we really want?"
In the two months since the problem was discovered, the Palo Alto Medical Foundation said it has been putting together an action plan for each of the 4,300 children impacted.
The list of of vaccines possibly degraded include DTAP, TDAP, IPV, Hepatitis A and B, Meningitis, Typhoid, Injectable Flu and TB Skin Test.
The medical foundation said it is providing all options free of charge.
The Palo Alto Medical Foundation in Los Gatos said it is updating all facilities to make its refrigeration process more exact.