The quest to unravel the mysteries behind the post-COVID-19 condition, also known as long COVID-19, took a step forward on Thursday with the launch of an internationally-coordinated attempt to capture standardized data on the condition.

The World Health Organization (WHO) and the International Severe Acute Respiratory and emerging Infection Consortium (ISARIC) announced a project to amass a so-called core outcome set (COS) to help build up a better picture of post-COVID conditions.

In a statement via the WHO, ISARIC said long COVID-19, which remains one of the lesser-understood aspects of the pandemic, was an "emerging global healthcare crisis."

Little is known about why some people, after coming through the acute phase of infection, struggle to recover and suffer ongoing symptoms including shortness of breath, extreme fatigue and brain fog as well as cardiac and neurological disorders.

Despite a "significant portion" of COVID-19 cases going on to suffer from long COVID, "the evidence for this condition is limited and based on small patient cohorts with short-term follow-up," ISARIC said.

"There is an urgent need for the development of a COS to optimize and standardize clinical data collection and reporting across studies [especially clinical trials] and clinical practice for this condition."

An international group of COS and post-COVID experts have put together a research program alongside the WHO and ISARIC, the statement said.

The project, entitled "Post-COVID Condition Core Outcomes," will start by surveying people living with long COVID.

The first phase, to be completed in the coming months, will focus on what outcomes should be measured. The second, to be completed in 2022, will look at how to measure these outcomes.