Estimates of the prevalence of long Covid – where symptoms persist for more than four or more than 12 weeks after infection, depending on the exact definition – vary dramatically.
Before getting to the estimates, what kind of symptoms are we talking about? All of the following have been reported: abdominal pain; cough; diarrhoea; fatigue; fever; headache; loss of taste; loss of smell; myalgia; nausea or vomiting; shortness of breath; and sore throat.
The ONS has documented that almost 14% of people who test positive for COVID-19 continue to report at least one symptom 12 weeks later. This estimate is based on data from the Coronavirus Infection Survey (CIS) – a large, random sample of UK residents living in private households. Here’s the ONS’s chart:
The control participants comprise individuals who took part in the CIS but were unlikely to have been infected. Note that only 2% reported at least one symptom on the relevant date. This seems to suggest that fully 12% of people who test positive for COVID-19 go on to experience long Covid (over and above the background rate).
However, while the CIS is a high-quality sample, the 12% figure isn’t necessarily correct. That’s because the symptoms are self-reported, and we don’t have any information on severity.
Due to the amount of media attention long Covid has received, CIS participants who tested positive might have been inclined to exaggerate their symptoms – to report things they normally wouldn’t have done. In other words, some of their symptoms might be more psychosomatic than physical.