Discolored Adimmune flu vaccine caused by defective stopper: CDC

Taipei, Oct. 15 (CNA) The discoloration of an Adimmune influenza vaccine dose found in Keelung on Saturday was caused by a defective rubber stopper and is considered an isolated incident, the Centers for Disease Control (CDC) said Monday.

A small brown mass measuring 1 mm x 0.5 mm was found on the rubber stopper inside the vial containing the discolored dose and had come in contact with the vaccine solution, said CDC Deputy Director-General Lo Yi-chun (羅一鈞), citing a report by Adimmune Corp.

The discoloration of the dose, which had turned pale yellow but remained clear with no cloudiness, was not caused by microbial contamination but rather 45 days of contact between a defective rubber stopper and the vaccine, Lo said.

The Keelung City Health Bureau first reported its discovery of the abnormal vaccine dose to the CDC on Oct. 12. It said the vaccine's discoloration was spotted and the vaccine withdrawn at the Qidu District Public Health Center earlier the same day.

Lo said at the time that the discolored flu vaccine dose was part of a batch of around 183,000 doses that had been distributed to health bureaus in six cities and counties: Taipei, Keelung, Taoyuan, Miaoli County, Hualien County and Taitung County.

After Monday's meeting with medical experts and representatives from Taiwan-based Adimmune, Lo indicated that 82,000 doses from that FSZA2408 batch had already been administered, while the remaining 101,000 doses in stock were temporarily suspended for use starting Oct. 12.

Inspections of those remaining doses from the FSZA2408 batch in the six cities and counties have been completed, with no abnormalities found, Lo said Monday. Also, no adverse events related to the FSZA2408 batch have been reported following administration.

The fate of those doses will be decided in a meeting of the Advisory Committee on Immunization Practices and the influenza prevention and control group on Oct. 23, Lo said.

Adimmune has also been tasked with providing a plan to replace the affected vaccines if necessary, he said.

For other batches of the Adimmune flu vaccine that have yet to be distributed to health bureaus, Lo said Adimmune has been instructed to conduct a visual inspection of each dose to ensure there were no abnormalities before distribution.

Adimmune issued a statement Monday evening in which it said the defect in the rubber stopper led to sulfur compounds within the stopper dissolving into the vaccine, leading to discoloration.

That was similar, it said, to an incident in 2018 when a dose of flu vaccine manufactured by French pharmaceutical company Sanofi was found to be discolored.

Describing the discoloration as a likely "isolated incident," Adimmune said the stoppers used in syringes containing the vaccine are made of rubber, which undergo vulcanization -- a chemical process that strengthens the rubber by adding sulfur -- during manufacturing.

Based on the acceptance standards provided by the supplier of the rubber stoppers, the probability of a defect occurring is one in 10 million, Adimmune said, noting that it is impossible to guarantee 100 percent defect-free stoppers even after inspection.

Adimmune supplies 50 percent of the government-funded flu vaccines each year, having provided over 20 million flu vaccine doses to the public to date, according to the company.

The incident will not affect the ongoing free influenza and COVID-19 vaccination program, which began on Oct. 1, Lo said on Oct. 12.

He said 6.254 million doses of flu vaccines procured from five different brands were still available under this year's program.