Treating critically ill COVID-19 patients with corticosteroid drugs reduces the risk of death by 20 percent, an analysis of seven international trials found on Wednesday, prompting the World Health Organization to update its advice on treatment.

The analysis — which pooled data from separate trials of low dose hydrocortisone, dexamethasone and methylprednisolone — found that steroids improve survival rates of COVID-19 patients sick enough to be in intensive care in hospital.

"This is equivalent to around 68% of (the sickest COVID-19) patients surviving after treatment with corticosteroids, compared to around 60% surviving in the absence of corticosteroids," the researchers said in a statement.