Kaiser Permanente’s Walnut Creek Medical Center on Monday said nearly 4, 000 of its patients may have got a little less of the correct COVID-19 vaccine dose last fall, SFGATE reported.

The health care provider is not getting in touch with about 3, 900 individuals who were vaccinated with Pfizer BioNTech COVID-19 from Oct. 25 to Dec. 10.

The recommended vaccine dose is at .30 milliliters but these people got between .01 and .04 milliliters less, Kaiser said in a statement.

The difference between the dose given and the recommended amount is minor, Kaiser and the U.S. Centers for Disease Control and Prevention’s medical experts said, noting that it cannot possibly cause less protection against the infectious disease.

But if the affected patients ask for another vaccine dose, Kaiser will be providing it.

It explained that the lesser dosage provided was an isolated case and was caused by a miscommunication between its staff.

“We took immediate steps to confirm that the issue was isolated and promptly retrained staff and validated their understanding of the correct procedure,” it said. “We are continuously monitoring so this does not happen again.”