What have we learned about long COVID?

Many people recover from a COVID-19 infection in a matter of days or weeks, but some go on to experience long COVID. This chronic health condition can cause more than 200 symptoms, from fatigue and shortness of breath to memory problems and difficulty thinking.

Approximately 7 percent of U.S. adults — about 17.8 million people — have had long COVID as of 2023, according to an article in the Journal of the American Medical Association. While long COVID varies in severity, the condition can be debilitating, affecting a person’s ability to work, attend school and function in their daily life.

In the second installment of this two part-series, find out what researchers — including those at the MultiCare Institute for Research & Innovation — have uncovered about long COVID and what’s left to learn.

What is long COVID?

Until recently, there was no universally accepted definition of long COVID, shares Mary Fairchok, MD, a pediatric infectious disease specialist at MultiCare Mary Bridge Children’s Hospital. This lack of agreement has made the condition difficult to study, track and treat.

In June 2024, the U.S. National Academies of Sciences, Engineering and Medicine defined long COVID as a “medical condition that persists for at least three months following a COVID-19 infection.”

Long COVID symptoms can:

• Affect any organ or part of the body
• Appear in people who experienced mild or severe initial infections, or experienced no sign of initial infection at all
• Grow progressively worse over time
• Wax and wane — appear to resolve or get better and then get worse again

A positive COVID test is not required to receive a diagnosis of long COVID, states the National Academies.

“Standardizing the criteria for long COVID makes it easier for researchers to obtain funds to study it,” Dr. Fairchok says. “It also supports health equity. People, whether or not they ever tested positive for COVID, can more easily access the care and services they need when there’s consensus on the long COVID criteria.”

Why do some people develop long COVID?

While long COVID has an official definition, understanding why it happens is a mystery researchers are still trying to solve.

One theory, Dr. Fairchok shares, is that the virus triggers an autoimmune response — where the immune system attacks the body’s healthy tissues along with the virus itself. Another theory is that the immune system is unable to completely clear the virus, leaving a persistent reservoir of virus particles in certain parts of the body like the brain or gastrointestinal tract.

A third theory is that the virus causes tiny blood clots that can damage blood vessels and obstruct circulation in certain parts of the body, leading to a wide array of symptoms, like brain fog when the clots occur in the brain, for example.

“Long COVID does seem to be decreasing in incidence as people develop more immunity,” Dr. Fairchok says. “But there will likely always be a pool of people that get long COVID due to how the virus interacts with their immune system.”

Who’s at risk for long COVID?

Anyone can get long COVID, including children, but the CDC reports that some people are at higher risk:

• Women
• Hispanic or Latino people
• People who experienced a severe COVID-19 infection
• People with underlying health conditions, such as obesity or diabetes, and those 65 or older
• People who are not up to date on COVID-19 vaccines

Each time you have a COVID infection, there’s a risk you will develop long COVID, which is one reason getting a yearly vaccination is so important.

“Multiple studies have shown that being vaccinated — and staying up to date with those shots — significantly reduces the risk of developing long COVID,” Dr. Fairchok says.

What a MultiCare study discovered about long-COVID

In June 2022, Jin Mou, MD, MSc, MPH, PhD, a senior research epidemiologist at the MultiCare Institute for Research & Innovation, launched a study in partnership with Michael Garrett, DNP, ARNP, FNP-BC, MHA, a board-certified family nurse practitioner at MultiCare, to learn more about long COVID.

Through this observational study, Dr. Mou and the research team examined electronic health record data of 153 MultiCare patients who tested positive for COVID-19 at a MultiCare facility and received monoclonal antibody treatment.

This type of treatment uses proteins, known as antibodies, made in a lab to help fight an infection. The patients were then surveyed twice about their health experiences. (Ninety-nine of the patients completed the second follow-up survey.)

“Long-COVID symptoms can be devasting. People from all over the country who are suffering from these symptoms have reached out looking for answers. It’s exciting to be able to share that vaccination, whether before or after an infection, does provide benefit for patients.”

In consensus with studies around the world, the research team found that vaccination appeared to be protective against many common long COVID symptoms. Patients who had one or more doses of a COVID-19 vaccine showed significantly decreased risk for experiencing symptoms related to:

• Cognitive functioning (thinking and memory)
• Physical functioning
• Dyspnea (shortness of breath)
• Fatigue

In fact, the MultiCare study found that two doses of a COVID-19 vaccine decreased the risk of fatigue symptoms by 57-80 percent, compared to study participants who never received a vaccine.

“Long COVID symptoms can be devasting,” Dr. Mou says. “People from all over the country who are suffering from these symptoms have reached out looking for answers. It’s exciting to be able to share that vaccination, whether before or after an infection, does provide benefit for patients.”

Another focus of the study was whether monoclonal antibodies offered protection from long COVID symptoms. These types of treatments have been used to help relieve COVID-19 symptoms during the initial phase of an infection and reduce the risk of hospitalization. However, the research team found that monoclonal antibodies do not appear to offer protection from long COVID.

“Future studies are going to be important for helping us pinpoint what exactly causes long COVID,” Dr. Mou says. “Ongoing research will also be critical in helping us develop effective therapies and treatments for patients.”