People who develop long COVID may be responding more strongly to a non–SARS-CoV-2 virus they encountered in the past than to SARS-CoV-2, a study by researchers at Harvard Medical School suggests.
Long COVID, also called postacute sequelae of COVID-19 (PASC), causes various symptoms that persist at least 4 weeks after the initial SARS-CoV-2 infection, they write in the preprint server medRxiv. Four authors explained their research into possible mechanisms of long COVID in an interview.
Dr. Jonathan D. Herman
“Immunity to non-COVID endemic coronaviruses may play a role in who develops PASC,” co–lead author Jonathan D. Herman, MD, PhD, said. “There’s still so much more we need to understand, but it is striking that back-boosting of immune responses to coronavirus OC43 was uniquely enriched in individuals with PASC.”
“In the study, individuals with PASC preferentially generated stronger responses to previously encountered cold-causing coronaviruses,” co–senior author Galit Alter, PhD, said.
Dr. Galit Alter
“Instead of generating strong SARS-CoV-2 immunity, they bolstered a response to a different coronavirus, potentially making their response less effective in clearing SARS-CoV-2. Surprisingly, most of the individuals had been vaccinated – and they still maintained this unusual antibody response – pointing to new therapeutic pathways to treat PASC,” Dr. Alter said.
Humoral immunity offers a clue to long-COVID origins
One-fifth of COVID-19 patients progress to long COVID, but which patients develop PASC and why are not well understood, the authors write.
“Antibodies represent powerful biomarkers that have been used for decades to diagnose disease. However, antibodies also provide a powerful source of information on previous infections. The use of antibody profiling, here, pointed to the presence of incomplete antibody responses to SARS-CoV-2 in individuals with PASC,” Dr. Alter said.
The researchers reviewed the medical records of patients in the Mass General Brigham health care system in Boston, including referrals from rheumatologists of participants diagnosed with COVID-19 outside the MGB system, starting on March 1, 2020.
They focused on patients with systemic autoimmune rheumatic diseases (SARDs) because their tendency toward inflammation and autoantibody production may make them more susceptible to PASC and enrich for specific inflammatory-driven endotypes.
All 43 participants had COVID-19 without hospital admission and SARDs. Patients treated only for fibromyalgia, osteoarthritis, mechanical back pain, gout, or pseudogout without a SARD were excluded from the study.
Overall, 79% of participants were female, 35% had rheumatoid arthritis, 19% had psoriatic arthritis, and 95% had received a COVID-19 vaccine.
The researchers used systems serology to perform comprehensive antibody profiling against SARS-CoV-2 and a panel of endemic pathogens or routine vaccine antigens.
Long-COVID patients had a distinct immune response
Overall, 17 patients developed PASC and 26 did not, and in those with PASC, they found a distinct humoral immune response. Patients with PASC:
- harbored less inflamed and weaker Fc-gamma receptor–binding anti–SARS-CoV-2 antibodies;
- showed a significantly expanded and more inflamed antibody response against endemic coronavirus OC43; and
- mounted more avid IgM responses and developed expanded inflammatory OC43 S2–specific Fc-receptor–binding responses, which were linked to cross reactivity across SARS-CoV-2 and common coronaviruses.
Dr. Jeffrey A. Sparks
“Strengths of the study include the detailed phenotypes of cases after COVID-19, particularly to classify PASC presence or absence, as well as the depth and breadth of antibody profiling. This allowed us to identify a humoral immune signature of PASC,” said co–senior author Jeffrey A. Sparks, MD, MMSc.
“However, the study was limited in its size to investigate different types of PASC, such as fatigue or lung symptoms, that may have biologic differences. Also, all patients in the study had a preexisting rheumatic disease,” he acknowledged.
Dr. Zachary Wallace
“A substantial portion of patients with COVID-19 will develop PASC, which can have substantial impact on health and quality of life,” said co–senior author Zachary S. Wallace, MD, MS. “Given the higher risk of COVID-19 in many patients with rheumatic disease, it is important to understand the etiology of PASC in this vulnerable population, to enable future diagnostic and therapeutic advances.”
Davey Smith, MD, professor of medicine and head of infectious diseases and global public health at the University of California, San Diego, in La Jolla, who was not involved in the study, called the findings interesting even though the results will not immediately affect patient care.
Dr. Davey Smith
“There may be a link between previous non–SARS-CoV-2 coronavirus infection and PASC,” he added. “Perhaps, by understanding why some people do and do not get PASC, we can develop treatments for the condition.
“This paper is a preprint and will need to go through peer review,” Dr. Smith said. “There are many elements that need to be scrutinized. For example, there is no definition of PASC that is universally accepted, so how did that play into this study?”
Mark Cameron, PhD, associate professor in the department of population and quantitative health sciences at Case Western Reserve University, Cleveland, called this a strong study from a strong group, although it is a preprint prior to peer review.
Dr. Mark Cameron
“In this initial study, the scientists focused on people who had rheumatic disease before getting COVID-19, knowing they are at higher risk for lasting complications and hopefully are more immunologically similar when diagnosed with long COVID – a single ‘endotype’ or group of patients with similar clinical symptoms and background,” he noted.
“Our immune system’s memory sometimes fails to effectively fight a new virus that looks too much like a virus it saw before. This ineffective immune response can set up various problems, including the poor recoveries we see in people with long COVID,” he said.
“OC43 probably emerged in the late 1800s and probably caused a pandemic of severe respiratory illness between 1889 and 1890, previously thought to be a flu,” Dr. Cameron recalled. “OC43 is still around as an endemic coronavirus, usually causing mild or moderate upper-respiratory infections.”
COVID-19 immunity is complex, and previous SARS-CoV-2 infection doesn’t guarantee we won't get COVID-19 again, especially as new variants emerge, added Dr. Cameron, who also was not involved in the study.
“This study may help us better understand the risks and possible mechanisms associated with COVID-19 and long COVID in the face of previous coronavirus infections,” he said. “It may also help guide future COVID-19 therapies and vaccines.”
The authors plan further related research.
The study received grant support and an anonymous donation. Dr. Alter, Dr. Sparks, and Dr. Wallace report financial relationships with the pharmaceutical industry. All other authors, and Dr. Davey and Dr. Cameron, report no conflicts of interest with the study. All experts commented by email.
* This story was updated 10/12/2022.