One of the many baffling issues with COVID-19 has been how it affects different people so differently. Comorbidities aside, doctors and scientists have been perplexed at why some people get such a severe case of infection, that they are critical while others seem to not even get the symptoms. Two National Institutes of Health (NIH)-funded studies have found previously unknown trouble spots in immune systems, which hamper some people's ability to fight the virus. A small percentage of people who suffer the most severe symptoms carry rare mutations in genes that disrupt their antiviral defenses. Another 10 per cent with severe COVID-19 produce rogue "auto-antibodies," which misguidedly disable a part of the immune system instead of attacking the virus.