Most adults with moderate-to-severe COVID-19 have a suppressed immune response against the novel coronavirus rather than life-threatening hyper-inflammation, according to a study which suggests steroids such as dexamethasone should be reserved for the sickest patients.

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Scientists, including those from St. Jude Children's Research Hospital in the US, assessed the levels of the immune system protein cytokines, and other health markers in 168 adults with COVID-19, 26 adults with flu and 16 healthy volunteers. They said more than 90 percent of the COVID-19 patients were hospitalised, and about half in the intensive care unit (ICU), while more than half of flu patients were admitted for treatment, and 35 percent were in the ICU. According to the research, published in the journal Science Advances, fewer than 5 percent of the COVID-19 patients, including some of the sickest individuals, had the life-threatening, hyperinflammatory immune response known as the cytokine storm syndrome.

The researchers explained that cytokine storms develop when excess or abnormally regulated levels of cytokine proteins in the body lead to hyperinflammation and tissue damage. While dexamethasone and other steroids are prescribed to treat cytokine storms, they said these drugs can backfire in patients whose immune response is already suppressed. "We did identify a subset of COVID-19 patients with the broadly upregulated array of cytokines. But, overall, the average person with COVID-19 had less inflammation than the average person with flu," said study co-author Paul Thomas from St. Jude Children's Research Hospital.

Based on the findings, the scientists said treatment suppressing inflammation might only be effective in a minority of patients with the hyperinflammatory profile. They believe the need of the hour is a fast, reliable, and inexpensive test to measure cytokines and identify patients who are most likely to benefit from dexamethasone treatment. "Directing immunosuppressive therapies to the small subset of COVID-19 patients who have an overactive immune response is the only way to know if these approaches are ultimately helpful," said Philip Mudd, another co-author of the study from the Washington University School of Medicine in the US.