A large study led by Kyung Hee University in Seoul shows that infection with SARS-CoV-2 significantly increases the risk of developing autoimmune inflammatory rheumatic disease for up to a year after infection.

The research, published in the Annals of Internal Medicine, shows that COVID-19 increased the risk for being diagnosed with an autoimmune inflammatory rheumatic disease by 25–30% compared with uninfected people or a group of individuals with previous flu, but not COVID infection.

“Emerging data suggest a higher risk for autoimmune inflammatory rheumatic diseases among patients with a history of COVID-19. However, these findings are based entirely on comparisons between groups infected with SARS-CoV-2 and those that are not, which might be biased by differences in health-seeking behavior and inherent risk factors within the groups,” wrote Dong Keon Yon, a professor at Kyung Hee University, and colleagues.

In this study, Yon and team used data from two medical claims databases in South Korea and Japan to test this theory. They included 10,027,506 Korean and 12,218,680 Japanese patients in the analysis who made claims between Jan 2020 and Dec 2021.

Patients who had COVID-19 were included (394,274 Korean people), as well as matched patients who experienced flu infection (98,596 Korean people) and uninfected controls.

Incident autoimmune inflammatory rheumatic disease was measured and included: rheumatoid arthritis, psoriatic arthritis, spondyloarthritis, systemic lupus erythematosus, Sjögren syndrome, systemic sclerosis, polymyalgia rheumatica, mixed connective tissue disease, dermatomyositis, polymyositis, polyarteritis nodosa, and vasculitis.

In the Korean cohort, the researchers found that previous COVID-19 increased the risk of incident rheumatic disease by 25% compared with uninfected individuals and by 30% versus influenza-infected patients after initial propensity matching to control for potential confounding factors. The risk was increased if the initial COVID-19 case was more severe. Similar patterns were seen in the Japanese cohort when the analysis was repeated.

Notably, the increased risk did appear to wane with time and was only minimally significant at 12 months or more after the initial SARS-CoV-2 infection. COVID-19 vaccination also seemed to decrease the risk for developing a rheumatic disease.

“This population-based cohort study shows that the increased risk for incident autoimmune inflammatory rheumatic disease extends up to 12 months after SARS-CoV-2 infection. Care strategies for patients who survive COVID-19 should pay close attention to [this], particularly after severe COVID-19,” concluded the authors.