Three out of the eight South Koreans who have shown abnormal reactions to potentially defective flu vaccines are children, the public health agency said Friday.

A total of 1,910 people were injected with the vaccines that were suspected to have been exposed to room temperature, according to the Korea Disease Control and Prevention Agency (KDCA).

Out of the eight people who have complained of symptoms that include headaches, chills and nausea, one is under the age of 10, two are teenagers, three are in their 30s and two are in their 50s, the KDCA said.

"Those symptoms were mild, and their conditions have improved," a KDCA official said. "But the relations between the vaccine injection, and the symptoms have not been proven yet."

Last month, the KDCA temporarily halted its plan to offer free seasonal flu shots after some of the about 5 million doses of flu vaccines were partially exposed to temperatures outside the storage range.

Inactivated vaccines should be stored in a refrigerator, and exposure to room temperature could result in decreased vaccine potency and increased risk of vaccine-preventable diseases.

But the safety of those vaccines exposed to room temperature has yet to be determined. (Yonhap)