South Korea has suspended its free seasonal flu vaccine program upon learning cold chain storage had been compromised during shipping process.

The Korea Disease Control and Prevention Agency (KDCA) said Tuesday some of about 5 million doses of flu vaccines set for infants and children were partially exposed to temperatures outside the storage range during distribution by Shinsung Pharm, a state-contracted vendor, raising concerns for its potency and safety.

As part of efforts to prevent a so-called twindemic, a convergence of the seasonal flu and COVID-19, the government had scheduled to provide free flu shots to around 19 million people, or 37 percent of the country`s population, including children, pregnant women and the elderly.

The KDCA said that it will conduct a quality test for the vaccines at issue for two weeks but fell short of specifying how many shots are affected.

In a worst-case scenario, a significant amount of vaccines would be affected, and this could cause a delay or cancellation in planned vaccination, experts warned.

The flu vaccine is produced in animal cells or fertilized eggs, and it takes 4 to 6 months to produce a batch of vaccines. Because of this time interval, a sudden supply vacuum cannot be closed immediately by vaccine manufacturers.

Inactivated vaccines like flu vaccines should be stored in refrigerators, and exposure to room temperature for a certain time period could result in a decrease in protein content, leading to a problem in vaccine potency and safety.

The KDCA said it will wait for the test results before deciding whether it will destroy all 5 million vaccine doses, adding it will make utmost efforts to ensure timely supply of shots for the elderly planned next month.

The government started a free flu vaccination on Sept. 8 for young children aged between 6 months and 9 years old. It said the already distributed shots have no quality problem.

By Seo Jin-woo and Minu Kim

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