South Korea is no longer using Celltrion’s Regkirona, the only COVID-19 antibody drug approved for use in the country, after it was shown to be ineffective against the omicron variant. Omicron now accounts for nearly all new infections here.

In a message to reporters Wednesday afternoon, the Korea Disease Control and Prevention Agency said it had stopped supplying Regkirona as of Feb. 18, confirming earlier media reports. The agency said the remaining stock of Regkirona will only be used for patients who are found to have variants other than omicron.

As a reason for restricting the drug’s use, the agency said that an in vitro study revealed Regkirona was “assessed to be unlikely to be active against omicron.”

Following the latest results a Ministry of Food and Drug Safety official told The Korea Herald that the terms of approval for Regkirona has been revised. “A desclaimer has since been added: Regkirona’s neutralizing ability is significantly diminished against omicron. But in circumstances where it is deemed to have benefits, it can be administered,” he explained.

The updated product information for Regkirona on the ministry’s website states that an in vitro analysis showed the drug retained activity against COVID-19 variants of alpha, zeta, eta and iota. On the other hand, its activity was reduced against beta, gamma, delta, kappa, epsilon and omicron.

With Regkirona out of the picture, other COVID-19 therapies available in Korea include Pfizer’s oral antiviral treatment, Paxlovid, and Gilead Sciences’ intravenous Remdesivir. But not all patients are eligible to receive them.

Per the disease control agency guidelines, Paxlovid is prescribed to patients in their 40s and up with certain health conditions. Remdesivir can be given to clinically vulnerable patients as young as 12 with mild to moderate symptoms.

“While it’s a shame that Regkirona’s neutralizing ability is weakened against omicron, we will continue to work to come up with a follow-up product that works against various variants,” a Celltrion official told The Korea Herald.

Korea plans on bringing in alternatives such as GlaxoSmithKline’s sotrovimab and AstraZeneca’s Evusheld, according to the KDCA accouncement Thursday. The agency said GSK’s request for an emergency authorization was under review with the Drug Ministry.

The move to take Regkirona off the front line had already been anticipated, according to earlier assessments by experts.

Dr. Oh Myoung-don, the head of the National Medical Centers’s clinical committee for emerging infectious diseases, citing an article in the science journal Nature, said omicron “incapacitates” many existing antibody drugs, Regkriona included.

The ascent of the new variant has caused an array of antibody drugs to be pushed off the shelves, with the exception of sotrovimab.

A month ago the US Food and Drug Administration amended its emergency use authorizations for COVID-19 antibody treatments from Regeneron and Eli Lilly to limit their use, as they likely do not work against omicron.

Critical care and respiratory disease specialist Dr. Kim Dong-wan of city-run Busan Medical Center said in a Jan. 7 phone call with The Korea Herald that Regkirona, which is developed to protect against the original Wuhan virus, “wasn’t working very well with delta patients.”

“With alpha, Regkirona still remained effective. But after delta took over, it had to be used in combination with corticosteroids like dexamethasone,” he said.

By Kim Arin (arin@heraldcorp.com)