The definition of long COVID used in interventional studies

There has been little consensus for a specific definition of long COVID, though several organizations have created varying ones. We sought to examine the definition of long COVID used in ongoing clinical trials.

We searched 'long COVID' and related terms on both PubMed and clinicaltrials.gov for randomized studies that either included patients with long COVID or had a persistent or long-term COVID-related outcome and abstracted long COVID definition components.

Of the 92 studies, a laboratory-only confirmed diagnosis of COVID-19 was stipulated in 54.3% (n = 50) studies. We found eight different time durations specified for how long symptoms needed to have occurred, ranging from 4 to 52 weeks, with 12 weeks being the most common (34.8%; n = 32). 35.9% (n = 33) did not specify a time duration. There were 57 different symptoms specified in total, with a median of one symptom identified per study (range 0-32). 8.7% of trials adhered to NICE or WHO definitions.

Standardized definitions of long COVID should be applied in studies assessing this condition to unify and harmonize research on this topic.