While primarily perceived as a respiratory disease, COVID-19 can apparently affect many different organ systems. Thus, its signs and symptoms have also been varied. The duration of illness is usually within the period of 14 days.
In most people, the disease manifests like a respiratory disease—meaning, cough, colds, runny nose, itchy or sore throat, fever, headache, muscle aches, and/or fatigue.
However, notable symptoms have also included the loss of (or even just an altered) sense of smell and/or taste, diarrhea, and vomiting.
Many people experience only a mild course of illness; however, in the minority of cases, the illness progresses and causes more serious complications. These can include pneumonia and respiratory failure (manifesting mainly as difficulty in breathing), heart problems including heart attacks, and blood clots in the brain or lungs (including embolisms and strokes). These can all be fatal.
People more at risk of developing a worse course of disease include the elderly, the immunocompromised, or those with co-morbidities, which includes a wide spectrum of conditions such as asthma, allergic rhinitis, respiratory allergies, diabetes, hypertension, obesity, autoimmune disorders, infectious diseases like HIV, and many diseases of the kidney, liver, heart, blood, and lungs.
A subset of infected people will experience no symptoms—otherwise known as asymptomatic disease.
Another subset of infected people will experience “Long COVID,” where they experience symptoms that last for a longer period of time, far beyond what most people experience. There have been many reports of previously infected people who continue to experience symptoms that range from chronic or recurrent fatigue, shortness of breath, prolonged distortions to the senses of smell and taste, or even cognitive dysfunction such as memory lapses, “brain fog” (or inability to concentrate), and changes in sleep or mood. Long COVID continues to be a subject of evolving study.