SEOUL, June 17 (Yonhap) -- South Korean health authorities on Wednesday cautioned against the efficacy of dexamethasone in treating the novel coronavirus, saying the widely used steroid should only be used as a supplementary treatment against COVID-19.

"Dexamethasone is a drug that reduces inflammation and does not fundamentally treat COVID-19," Jeong Eun-kyeong, head of the Korea Centers for Disease Control and Prevention (KCDC), said during a daily briefing.

The remarks came after scientists at the University of Oxford announced that dexamethasone reduces the risk of death in seriously ill COVID-19 patients by about 33 percent.

The World Health Organization also said dexamethasone is the first treatment to be shown to reduce mortality in virus patients requiring oxygen or ventilator support.

"We think dexamethasone is not a drug that is as effective as other treatments (such as remdesivir) but is a sort of supplementary treatment," Jeong said.

The KCDC also cautioned against possible side effects, noting that other steroids have previously been used to reduce inflammation in COVID-19 patients.

The country's drug watchdog, the Ministry of Food and Drug Safety, has so far approved the use of 79 dexamethasone-based drugs.