People taking medications that suppress the immune system overall do not have a higher risk of dying from COVID-19 or being put on a ventilator than those not taking these drugs, according to a study published in The Lancet Rheumatology journal.

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The team led by researchers at Johns Hopkins University in the US analysed electronic health records of adults hospitalised with COVID-19 from January 2020 to June 2021 in the US.

The study included 222,575 individuals, including 16,494 patients who had been on immunosuppressive medications prior to hospitalisation. The researchers separated these medications into 17 classes and found that none were associated with a significantly increased risk of being put on a ventilator -- an indication of severe COVID-19 illness.

"In general, people taking immunosuppressive medications may be reassured that they can safely continue to do so during this pandemic," said study lead author Kayte Andersen, a doctoral candidate at Johns Hopkins University Bloomberg School.

"These findings are encouraging and important, given how commonly these medications are used," said G Caleb Alexander, a professor at the Bloomberg School's Department of Epidemiology. At the start of the pandemic, people who take immunosuppressive drugs for organ transplants, autoimmune diseases, cancers and other conditions were considered as being at potentially increased risk of severe outcomes, given their weakened immune systems.

On the other hand, some of the damage to lungs and other organs in severe COVID-19 comes less from direct viral damage and more from immune overactivation, the researchers said.

By the summer of 2020, doctors were treating severe COVID-19 with immunosuppressive drugs such as dexamethasone, they said. The researchers noted that it was not initially clear whether the long-term use of immunosuppressive drugs increased or decreased the risk of severe COVID-19.

In a smaller, preliminary study published earlier this year, the team found no significant association between the chronic use of immunosuppressive drugs and ventilator or mortality risk. This suggested any increased susceptibility to infection and viral spread may be balanced by a decreased susceptibility to harmful inflammation, the researchers said.

The latest study, drawing from a nationwide dataset gathered by the National COVID Cohort Collaborative, covered a sample of COVID-19 patients that were over 100 times larger than the preliminary study. The researchers found that overall, hospitalised COVID-19 patients taking immunosuppressive drugs did not face significant increases in the risk of COVID-19 death compared with non-immunosuppressed hospitalised patients.

Of the 303 drugs examined, they found that only one drug, rituximab, a monoclonal antibody that targets antibody-producing B cells, was associated with a substantially increased risk of death compared to medically similar hospitalised COVID-19 patients. Rituximab is used for serious medical conditions like cancer or an autoimmune disorder that has not responded to other treatments.

The analysis included 153 cancer patients taking rituximab and 100 patients taking rituximab for a rheumatologic condition. After accounting for sex, age, medical conditions, and other factors, the risk of death for the cancer patients taking rituximab was more than double and the risk for patients with a rheumatologic condition was nearly three-quarters higher compared with medically similar people in the study.

"Given the finding, patients taking rituximab should discuss their options with their doctor," said Andersen. "At a minimum, people who take rituximab should continue to protect themselves from developing COVID-19. It also makes it all the more important that people around those taking rituximab get vaccinated," she added.