Long COVID is a catch-all term for a wide range of symptoms that can include brain fog, fatigue and shortness of breath months or even years after a COVID-19 infection. But why do some people get it and others don’t?

Definitions are fuzzy, with some organizations saying long COVID, also called post-COVID syndrome, is the presence of symptoms four weeks after infection and others defining it as symptoms seen after three or more months post-infection.

IMAGE: Abjad

But researchers are beginning to peel back the layers to fully understand the phenomenon.

Women more affected

The U.S. government in August 2022 launched its National Research Action Plan on Long COVID to research the syndrome and support the people affected. And in October 2022 the U.S. Census Bureau and National Center for Health Statistics published a survey that illustrates the broad reach long COVID – defined in the survey as having symptoms three months or more after infection  – can have.

Among the survey findings:

Women are more likely to get long COVID than men are, perhaps due to hormonal and immunological differences between men and women. They are also more likely to experience severe symptoms.

During the pandemic, 17 percent of U.S. women had long COVID, compared with 11 percent of U.S. men.

Among all women, 2.4 percent had symptoms severe enough to significantly limit their daily activities. Of all men, 1.3 percent reported experiencing symptoms that reduced their ability to perform day-to-day activities, according to the survey.

By early 2023, 15 percent of all U.S. adults had reported symptoms of long COVID; 6 percent reported current symptoms. 

Are you vaxxed?

Meanwhile, a study published in October 2022 in JAMA finds that vaccination may reduce your chances of getting long COVID. But there are no points for half measures.

The study finds that completing the vaccination series before contracting the virus seems to reduce the risk of long COVID. Partial vaccination, however, such as taking one jab in a series of two, did not show any reduction in risk.

Claire J. Steves, one of the authors of a 2022 Lancet paper, tells KUST Review that one of the takeaways of her study is how important it is to get vaccinated.

“Back in October 2021 we showed how vaccination reduces the risk of long Covid. That’s mainly because still the strongest driver of risk of long Covid is the severity of initial illness. Vaccination really reduces this.”

In the JAMA study, fatigue is listed as the most common symptom, followed by loss of smell, “brain fog” and shortness of breath. The frequency of symptoms was also associated with sex, with women being more likely to report loss of smell, cognitive symptoms, anxiety and sleep disruptions.

Researchers from Kings College London, who published their results in July 2022, found three groups in the long COVID cohort based on people who reported their symptoms via an app:

The largest group reported “brain fog,” headache and fatigue.

IMAGE: Abjad

A second group reported symptoms most common in the early stage of the pandemic, before vaccinations were available. These were respiratory symptoms such as severe shortness of breath and chest pain.

And a smaller third group reported a range of symptoms including heart palpitations, changes in skin and hair and muscle pain.

IMAGE: Abjad Design

The variant and severity of illness

The variant contracted and severity of initial illness also make a difference.

A study presented to the European Congress of Clinical Microbiology and Infectious Diseases in April reported that those who were infected during the Omicron waves were as likely as people who’d never been infected with COVID-19 to experience lingering symptoms.

Those infected by the original variant were 67 percent more likely to experience lingering symptoms than those who never had a COVID infection.

And as Steves previously noted, the severity of initial illness is a factor. So preventing a severe infection is important. Why? Again, still a mystery. But Mayoclinic.org suggests that inflammation and organ damage from a severe illness could be a driver of long COVID.

Other factors

As with many illnesses, it’s complicated by many other factors. A study published in Nature Medicine finds other risks for long COVID include ethnicity, socioeconomic deprivation, smoking, obesity and other comorbidities.

Previous studies had indicated that age was an issue, but in a February paper for Gerontology & Geriatrics, Columbia University’s Ray Marks says there just isn’t any evidence. “Age alone cannot be a factor because the condition appears to randomly affect older as well as younger COVID survivors, regardless of vaccination or health status,” he writes. 

Mental health link

Long COVID might also have a link to mental health, although there is still some question about whether it is a cause or effect. Patients with long COVID were about twice as likely to get a prescription for an antidepressant for the first time within 90 days of their initial diagnosis, according to an analysis for Reuters conducted by health-data company Truveta.

Researchers are now asking whether changes in brain chemistry are causing the issue or if patients are experiencing distress as a result of a loss of function.

Things are looking up

The good news, however: The percentage of people who have had COVID and have long COVID symptoms has declined. It was 19 percent in June 2022 but was 11 percent in January 2023, according to the Kaiser Family Foundation.