More than 100 South Korean have been injected with seasonal flu vaccines that should not have been administered due to storage problems, but there have been no reported side effects, health authorities said Friday.

The Korea Disease Control and Prevention Agency (KDCA) said hospitals and public health centers in Seoul and three other areas gave flu shots to 105 people with some of the vaccines that weren't supposed to be administered after being exposed to room temperature.

The agency said the affected people have been informed of their injections, and it was monitoring whether they were showing any side effects.

Yet, none of the people injected with such vaccines have showed extraordinary reactions, the agency said, adding it will keep close tabs on those people.

Several clinics and hospitals in Seoul and other regions used the problematic shots, the KDCA said.

The agency said it was initially testing 750 doses of the exposed flu vaccines in five different regions and planned to carry out an additional test.

The KDCA said it has signed contracts with other distributors to ship safe vaccines besides Shinsung Pharm. Co., the distributor of such vaccines. The company earlier said 170,000 doses are presumed to have been exposed while being moved between vehicles.

Starting earlier this month, the country has provided free flu shots, mostly for young children, in an effort to increase the number of immunized people.

The government was to provide free flu shots to around 19 million people, or 37 percent of the country's population. Children between 6 months and 18 years old, pregnant women and those aged 62 years old or above were included.

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

Inactivated vaccines should be stored in refrigerators, 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.

KDCA Commissioner Jeong Eun-kyeong said the agency will complete a quality test on those exposed vaccines as quickly as possible and do its utmost to provide safe flu shots to people.

The KDCA assured that there is very slim chance of the problematic flu shots causing health risks.

"There is little possibility of the vaccines being contaminated as each vaccine is sealed in a disposable syringe for each person's use," Jeong said.

The KDCA had said that if the exposed vaccines pass quality tests, they will be administered to those in the 13-18 age bracket, followed by the older demographic. (Yonhap)