A study in Nature of more than 2,200 intensive care patients has identified specific genes that may hold the answer.
They make some people more susceptible to severe Covid-19 symptoms.
The findings shed light on where the immune system goes wrong, which could help identify new treatments.
These will continue to be needed even though vaccines are being developed, says Dr Kenneth Baillie, a consultant in medicine at the Royal Infirmary in Edinburgh, who led the Genomicc project.
Source : BBC