According to data from millions of users of the ZOE COVID Symptom Study app, there are at least six distinct clusters of symptoms. And some people become mildly, severely or fatally ill while others appear to have no symptoms at all - a phenomenon known as ‘asymptomatic COVID’.
Here’s what we know so far.
The COVID Symptom Study shows a relatively low number of truly asymptomatic cases
Estimates of the number of people who have COVID-19 but do not experience symptoms (asymptomatic) vary wildly from 5-96%.
But many studies reporting a high number of asymptomatic cases focus on the three key symptoms and/or only report the symptoms experienced on the day of the COVID-19 test instead of the entire infection period.
We found one in four (25%) had antibodies, indicating they had been infected, but hadn’t recorded any of the three ‘classic’ symptoms of COVID-19.
When we looked more closely at the number of people with antibodies who didn’t record any symptoms at all - including symptoms such as fatigue, headache or diarrhoea - that number dropped to around one in five, suggesting a 20% rate of asymptomatic cases.
Our estimate of truly asymptomatic cases is lower than many other studies because we looked at a wide range of symptoms over the entire course of infection.
However, this may still be an overestimate because at the beginning of the pandemic we didn’t ask questions about skin rashes in the app, which we now know are present in around 8% of positive cases. So the true asymptomatic rate may well be lower than 20%.
In some people, less typical symptoms like rashes or delirium are the only symptoms they experience.
Based on our analysis, we believe that people who have any suspicious symptoms should self-isolate and get tested, even if they don’t have the ‘classic triad’.
Understanding the true extent of COVID-19 infection is essential for containing the pandemic
We don’t know how many people have had COVID, so it’s difficult to say how many experienced symptoms
The rate of asymptomatic infections may be lower than we think, especially if we look at a wide range of reported symptoms over the entire infection period
Looking for a wider range of symptoms could help us find more COVID-19 cases
Symptom tracking and testing are vital for identifying cases of COVID-19 and stopping the spread of the disease.
To learn more about COVID-19 and the best ways to contain the disease, we need your help. If you haven’t already, download the app now, log your symptoms daily (even if you are well), and be part of the largest study of COVID-19 symptoms in the world.