For many, catching SARS-CoV-2 means an unpleasant few weeks of aches, coughs, and fatigue. In roughly one in every five cases, however, the discomfort endures for months on end.

What puts some individuals at greater risk of an acute infection lingering as long COVID has been far from clear.

A team of experts from across the US analyzed the records of 4,708 US adults infected by SARS-CoV-2 between April 2020 and February 2023. Around one in five still had difficulties with COVID-19 after three months – the threshold for long COVID.

Long COVID was found to be more common in women, and those with previous cardiovascular disease issues. It was also less common in those who had been vaccinated, and in people with the less severe Omicron variant of the infection.

"Our study underscores the important role that vaccination against COVID has played, not just in reducing the severity of an infection but also in reducing the risk of long COVID," says Elizabeth Oelsner, an epidemiologist at the Columbia University Irving Medical Center.

While some health conditions like chronic obstructive pulmonary disease and a history of smoking were linked to longer recovery times, these became insignificant once other risk factors were also factored in.

Severe infections and longer recovery times were also found to be more common in American Indian and Alaska Native participants, adding to what we already know about racial and ethnic disparities with COVID-19.

Some of these risk factors, including a higher long COVID risk for females and a lower risk for vaccinated individuals, have been reported before. However, in this sample the researchers didn't find any significant link to mental health issues – even though long COVID results in some major changes in the brain.

"Although studies have suggested that many patients with long COVID experience mental health challenges, we did not find that depressive symptoms prior to SARS-CoV-2 infection were a major risk factor for long COVID," says Oelsner.

With a better knowledge of who is most at risk from long COVID, it becomes easier for researchers to figure out why it's happening in certain people – and from there what sort of treatments might be effective against the condition.

As most of the world tries to move on from the pandemic, millions worldwide with persisting COVID-19 symptoms and society at large stand to benefit from ongoing research on the disease.

"Our study clearly establishes that long COVID poses a substantial personal and societal burden," says Oelsner.

"By identifying who was likely to have experienced a lengthy recovery, we have a better understanding of who should be involved in ongoing studies of how to lessen or prevent the long-term effects of SARS-CoV-2 infection."

The research has been published in JAMA Network Open.