Even bone marrow may not be a safe harbor from the ravages of COVID-19, according to a study that found previously unrecognised changes in newly produced immune cells, called monocytes, released into the blood from bone marrow.

To learn more about how the body responds to COVID-19, researchers obtained serial "snapshots" of patients' immune health by analyzing their immune cells at multiple points during their hospital stays.

In COVID-19 patients with more severe disease, the monocytes do not function properly, researchers reported last week in Science Immunology.