The greatest study of its kind suggests that contracting COVID-19 increases the likelihood of having an autoimmune disease by 43% in the months after the infection.
Anuradhaa Subramanian, a research fellow in health informatics at the University of Birmingham who was not involved in the study, stated, “The effect of this work is significant — it’s the strongest evidence so far answering this topic of COVID-19 and autoimmune disease risk.” The new study was published on January 26 on the preprint repository medRxiv but has not yet undergone peer review (opens in new tab).
Previous research has connected COVID-19 to a higher risk of autoimmune diseases, in which the immune system erroneously targets healthy body components. The research, however, was restricted to tiny studies that concentrated on just a few illnesses, including Guillain-Barre syndrome, which affects nerve cells, and autoimmune hemolytic anemia, which damages red blood cells.
Now, researchers are investigating how the infection may increase the likelihood of getting any of 30 autoimmune disorders. They have examined the health records of 640,000 people in Germany who contracted COVID-19 in 2020 and 1.5 million people who unknowingly contracted the coronavirus in that year.
They looked at how frequently autoimmune disorders were discovered in persons three to 15 months after they had tested positive for COVID-19. These rates were contrasted with those of persons who had not contracted COVID-19. Each group comprised about 10% patients who had autoimmune disorders that were already present.
During the follow-up period, more than 15% of those who had contracted COVID-19—as opposed to around 11% of those who hadn’t—developed an autoimmune disease for the first time among those without a prior history of autoimmunity. In other words, autoimmune illness was 43% more likely to occur in the COVID-19 group than in the control group.
Among those who already had autoimmunity, COVID-19 infection increased the risk of getting another autoimmune disease by 23% throughout the follow-up period.
Vasculitis, which causes inflammation of the blood vessels, was the condition most strongly associated with COVID-19; the previously infected group had a 63% higher rate of arteritis temporalis than the uninfected group did. Prior COVID-19 infection was also highly associated with autoimmune-driven issues with the thyroid, a butterfly-shaped organ in the throat that releases hormones, the skin ailment psoriasis, and rheumatoid arthritis, which causes joint swelling.
There are many hypotheses as to how COVID-19 might trigger autoimmunity, and it’s possible that different mechanisms affect different organ systems, the researchers noted. “These findings just cannot be ignored,” Subramanian said. “We need to pursue research into how COVID-19 is potentially triggering autoimmunity.”
In order to implement prevention strategies and early treatments to reduce associated morbidity and mortality, Jagadeesh Bayry(opens in new tab), a professor of biological sciences and engineering at the Indian Institute of Technology Palakkad who was not involved in the study, said: “Understanding how COVID-19 impacts autoimmune disease risk.”
Future studies should also examine these links in diverse populations, beyond people living in Germany, Subramanian said. More research is needed to establish what effects are specific to COVID-19 because other viral infections, including influenza(opens in new tab), have been linked to autoimmune disease.
Despite the substantial sample size, Dr. Atsushi Sakuraba, an associate professor of gastroenterology at the University of Chicago who was not involved in the study, noted that the study “just indicates a connection between COVID-19 and autoimmune illness but doesn’t prove causality.”
The study can’t show whether different coronavirus variants are linked to a higher or lower risk of autoimmune disease, or how COVID-19 vaccination affects that risk. Another limitation is that there may have been individuals in the study’s uninfected group who actually caught COVID-19 but developed little to no symptoms, and thus didn’t know they had been infected.