Doctors in Hong Kong reported on Tuesday that a side-effect of the Covid-19 vaccines has led some people to believe they had cancer.

The founder of the Hong Kong Breast Cancer Foundation, Dr Polly Cheung, said it’s because coronavirus vaccination could lead to enlarged lymph nodes, which might be mistaken as cancer in PET scans.

Some people who have been vaccinated against Covid-19 were reported to receive false positive results in subsequent PET scans, she said.

The scan involves the injection of a radioactive substance into a person’s veins. The images produced on the scan would then show any abnormal areas.

“I have a patient who’s on cancer surveillance so she had a PET scan. The scan showed a number of lymph nodes enlarged. She was so frightened and thought it might be cancer recurrence,” Cheung said.

The doctor said a subsequent ultrasound showed the patient did not have cancer, and the size of her lymph nodes returned to normal a few weeks later.

Cheung advised people to wait for at least a month after Covid-19 vaccination before undergoing a PET scan.