Weekend Reads | Trying to Understand Long COVID

by Kevin Schofield

For many people, contracting COVID-19 is the gift that keeps on giving, with symptoms persisting potentially for months after the initial illness. People with "long COVID" complain about some combination of fatigue, body pain, and ongoing respiratory and cognitive problems. However, the exact symptoms vary from person to person, as does the length of time they persist. That's made long COVID a huge challenge for the medical community to understand, diagnose, and treat. But as time has passed, more long COVID cases have been documented, and more studies have been completed, we're starting to get a better understanding of its parameters.

This weekend's read is a new "meta-study" by the Global Burden of Disease Long COVID Collaborators, looking at 54 long COVID studies and two medical records databases containing data on 1.2 million COVID patients. It does three important things: it sorts out all of the frequently reported "long COVID" symptoms into three related clusters; it provides statistics on what percentage of COVID patients went on to display symptoms of long COVID; and it estimates the length of time patients suffer from long COVID. Having multiple studies and large patient databases gives us more faith in the reliability of the statistics: One individual study may have flaws or biases, but aggregating a large number together will tend to make those flaws disappear into background noise.

The researchers cluster the wide range of reported long COVID symptoms into three categories: respiratory problems, cognitive problems, and fatigue with bodily pain or mood swings. Just thinking about how different those medical conditions are, we can imagine the difficulty for doctors in deciding that they are all "long COVID" — let alone in trying to understand the mechanism through which the coronavirus could cause such a wide range of long-lasting symptoms.

Just over 60% of long COVID patients experience just one of these three clusters of symptoms: One-third have respiratory symptoms, 18% have fatigue, and 10% have cognitive symptoms. About 30% showed symptoms from two clusters, and around 9% had symptoms from all three. Respiratory symptoms are by far the most common, with 60.5% of long COVID patients suffering them either with or without other symptoms.

While symptomatic COVID cases are more common among men than women, long COVID is more common among women than men. Also for reasons unknown, long COVID affects men and women over age 20 more than younger people.

The data also shows that more serious COVID cases increase the likelihood of long COVID following. Overall, less than 5% of men (over age 20) and less than 10% of women displayed symptoms of long COVID, but those rates are around four times higher for those who had been hospitalized with COVID, and even higher for those who end up in the ICU (35.8% of men and 51.9% of women).

For those who were not hospitalized with COVID, the mean length of time for subsequent "long COVID" was four months, but for those who were hospitalized, the length increased to nine months.

While the researchers don't specifically talk about the effect of vaccinations on long COVID, we know getting vaccinated substantially reduces the likelihood of symptomatic COVID and hospitalization from the disease. Since the statistics above tell us that those who are hospitalized with COVID have both a much higher rate of suffering from long COVID and a longer length of time that they experience it, we can infer that getting vaccinated will provide important protection from both COVID and long COVID: not an assurance that you won't get them, but there should be fewer and lighter symptoms, and those symptoms should clear up faster.

There is still much we don't know about long COVID, starting with what exactly causes it (and the mechanisms may be different for the three clusters of symptoms). We also still don't have proven, effective treatments. But we are finally starting to understand who is at risk for it, how long it's likely to last, and what steps we can take to lessen our risk.

Estimated Global Proportions of Individuals With Persistent Fatigue, Cognitive, and Respiratory Symptom Clusters Following Symptomatic COVID-19 in 2020 and 2021

Featured image by Pete Hansen/Shutterstock.com.