The efficacy and safety of thalidomide combined with low‐dose hormones in the treatment of Severe COVID‐19  Placebo, drug: thalidomide  COVID‐19 thalidomide  40, all, 18 years and older  Treatment  Placebo comparator: control group α‐interferon: nebulized inhalation, 5 million U or equivalent dose added 2 ml of sterile water for injection, 2 times a day, for 7 days; abidol, 200 mg/time, 3 times a day, for 7 days; methylprednisolone: