US researchers have found that an abnormally suppressed immune system may be to blame for long Covid-19 and not a persistently hyperactive one previously thought. In a subset of persons who recover from the initial Covid illness, various symptoms persist, such as fatigue, mental haziness, and shortness of breath, which can be debilitating and last for months. This is generally classified as long Covid, although symptoms vary widely and this syndrome is probably not a single disease entity. Limited understanding of its causes, however, makes finding ways to treat the condition particularly diff...