RECOVER biosamples and data advance understanding of what may cause Long COVID

Pathobiology studies investigate the processes in the body (biological mechanisms) that can lead to the development of health problems. In addition to advancing our understanding of what can cause Long COVID, RECOVER pathobiology studies can build upon and bridge findings from other types of RECOVER research. In this way, pathobiology studies can produce insights that could lead to breakthroughs in diagnosing, preventing, and treating Long COVID.

Over the next 6 to 8 months, one of these pathobiology studies will focus on viral persistence, which is defined as when SARS-CoV-2 (the virus that causes COVID-19) stays in the body for a long period of time following initial infection. Researchers hope to identify the specific types of Long COVID that are caused by viral persistence. 

The study will connect 2 different kinds of data:

• The results of tests performed on the tissue, blood, and saliva samples (biosamples) collected from adults taking part in RECOVER observational studies.
• Survey responses about Long COVID symptoms and their severity shared by these same adult participants. 

Michael Peluso, MD, MHS, is one of 3 principal investigators leading this pathobiology study. He explained that there are 4 critical components to its design.

1. Measuring how much persistent SARS-CoV-2 is present in people with Long COVID.

Pathobiologists have a variety of tools available to perform detailed analyses (assays) of blood samples. These assays enable pathobiologists to detect and measure the precise amounts of substances contained in blood samples. One of this study’s goals is to determine the best ways to measure persistent SARS-CoV-2 in the blood.

To make this determination, the study team will use assays that have not yet been tried on RECOVER biosamples. “Prior studies have suggested that some of these measurements are potentially useful, but none of those studies were designed to really be definitive,” Dr. Peluso said. “They were exploratory or early phase studies.”

These assays will also include direct and indirect measurements of persistent SARS-CoV-2 virus. Direct measurements include the virus itself as well as pieces of the virus, like viral proteins or viral RNA (ribonucleic acid), which is what a virus like SARS-CoV-2 uses to make copies of itself. Indirect measurements consist of evidence that the body’s immune system is sensing the virus. That evidence includes the activation and circulation of specific cells (like T and NK cells) the body produces to fight the SARS-CoV-2 virus.

“We are trying to determine how these direct and indirect measurements relate to each other,” said Dr. Peluso. “We also want to know which measurements or combinations of measurements might be most useful in distinguishing people with Long COVID from people who have returned to their prior health status after COVID.” 

2. Testing biosamples collected from a large number of research participants.

Another key component of the project is that most of the measurements of viral persistence will be performed in high throughput. High-throughput assays use simplified processes and machine-automated procedures to allow for many tests to be performed in short periods of time. 

One of the chief benefits of high-throughput assays is that they allow researchers to test a large number of biosamples at reasonable costs. Large sample sizes are important so that researchers can avoid drawing a conclusion based on chance or random occurrences. “Our laboratory collaborators have developed high-throughput assays that give us the opportunity to conduct studies with larger sample sizes than is typically possible, which we believe will lead to more definitive results,” Dr. Peluso said.

3. Studying specific Long COVID symptoms.

Long COVID affects everyone differently. Research, including studies led by RECOVER researchers, suggests that there are unique types (phenotypes) of Long COVID marked by individual symptoms or combinations (clusters) of symptoms. 

Each person included in this pathobiology study will be assigned to a group associated with one of several Long COVID phenotypes. 

“Rather than lumping everybody together as having Long COVID and trying to see if there is a single cause for all of the different ways Long COVID can affect people, we believe that a more fruitful approach is to study each of the most common symptoms separately,” explained Dr. Peluso. “So, we are drawing from the large number of participants in RECOVER to identify hundreds of people who have consistent, debilitating fatigue, or consistent, debilitating trouble breathing, or consistent, debilitating brain fog (having trouble thinking clearly, concentrating, or remembering things), as well as other symptoms.” 

Dr. Peluso and his fellow researchers also plan to share their study’s Long COVID phenotype definitions with other pathobiologists. Doing so will enable RECOVER scientists studying the same set of biosamples to look for patterns and trends across multiple sets of data and findings.

4. Comparing people still experiencing Long COVID symptoms to people no longer experiencing Long COVID symptoms. 

Using the massive amounts of data RECOVER has collected, this pathobiology study will include both people with and without Long COVID. Researchers will compare viral persistence measurements between:

• Multiple groups of people experiencing different Long COVID symptoms.
• A single group of people no longer experiencing the Long COVID symptoms they reported having when they began taking part in RECOVER research.

Also known as the case-control approach, this element of the study’s design will help researchers focus on the effects of persistent SARS-CoV-2 versus other health conditions or other possible causes of Long COVID.

This pathobiology study will give researchers an opportunity to better understand what underlying biological mechanisms can cause specific symptoms of Long COVID in some people but not others. But Dr. Peluso emphasized that the study’s long-term goal is to help translate what researchers learn about viral persistence into improvements in Long COVID care. 

“We believe, based on the evidence that RECOVER has already generated, that viral persistence causes some types of Long COVID in some people,” Dr. Peluso said. “Confirming that belief with even more evidence will be a big step on the pathway toward being able to develop diagnostic tests for Long COVID.”