Around 90% of long COVID sufferers started with a mild bout with the coronavirus, according to a recent study.

Researchers sought to determine how many people who had mild symptomatic SARS-CoV-2 infections in 2020 and 2021 developed long COVID symptoms around three months after their initial illness.

They conducted an observational analysis using pooled data from 54 studies and two medical record databases with records for more than 1.2 million individuals from 22 countries. They examined those who reported at least one of the three most commonly reported long COVID symptoms —fatigue with body pain or mood swings, cognitive problems and respiratory problems.

After analyzing all the data, the team presented modeled estimates of the proportion of individuals who reported long COVID symptoms at least three months after their symptomatic mild infection. They presented their findings in a study published in the peer-reviewed journal JAMA.

The researchers found that a staggering 90% of people with long COVID initially only had mild COVID-19 infection. The long-term symptoms they developed impacted their health and daily functioning.

However, they also found that patients who were hospitalized due to COVID-19 had a greater risk of developing long COVID than those who were not hospitalized. But since the majority of COVID-19 cases did not require hospitalization, the ones that arose from mild infections became more pronounced, the team noted in their research brief published via The Conversation.

The scientists said they focused on long COVID for their study since very little is known about the condition even though it has been three years since the coronavirus pandemic started. They said finding effective and affordable treatments for people with long COVID should be a priority in the medical community because many sufferers struggle to get back to their normal lives and keep their work.

This week, Medical News learned about a new machine learning tool that could help scientists understand how long COVID patients develop their chronic symptoms. The software is designed to analyze entries in electronic health records and spot symptoms common among long COVID patients, so they can be classified into defined subtypes. The proponents expect the tool to help clinicians develop tailored therapies for each group.