Nearly four years since COVID-19 made headlines, new discoveries continue to reshape our assumptions about the disease. Siew-Wai Fong, a Senior Scientist at A*STAR Infectious Diseases Labs (ID Labs) cites the example of the populations we consider at high risk for ‘long COVID’: a constellation of changes to the body that can linger for months to years after infection, with potentially debilitating effects.
“Initially, the focus of long COVID research was on individuals who had severe acute illness; we now know it can also affect people who had mild or asymptomatic disease,” said Fong.
Many aspects of long COVID remain a mystery: its causes, why it impacts some individuals over others, or why it manifests in varied symptoms ranging from brain fog to cardiovascular disease. Even the question of how common it is can be difficult to answer: studies report between 13 to 87 percent of patients who had COVID-19 deal with persistent symptoms.
Part of the issue is that long COVID can be difficult to diagnose. According to Fong, some patients may appear completely recovered on the outside, but show subtle signs of COVID-linked inflammation in their pulmonary, cardiac and renal systems.
“If we can detect long COVID earlier in its course, we can start treatment before it further impacts a patient’s health,” said Fong.
Working with the National Centre for Infectious Diseases, Singapore; National University of Singapore; Changi General Hospital; and Tan Tock Seng Hospital; A*STAR researchers tracked how post-COVID complications progressed in survivors of severe disease. They also searched for immune biomarkers that can be used to identify patients likely to have persistent inflammation.
Changes in immune mediator levels observed in a cluster of 78 patients with COVID-19 up to 12 months after their initial onset of illness. Previous studies have associated MCP-1, MIP-1β and IP-10 with chronic fatigue syndrome—a common symptom of long COVID—while other biomarkers have been linked to inflammatory effects in blood vessels and nerve cells.
The researchers recruited 78 patients in Singapore who were hospitalised with COVID-19 in the pandemic’s early phases. Over two years after their discharge, the researchers collected blood samples and self-reported data on any symptoms experienced.
A year into the study, 29 participants reported symptoms such as lingering cough and fatigue. Their blood samples revealed high levels of cytokines: immune mediators known to promote inflammation. The team also noted that patients with persistent inflammation showed distinctive levels of T cell differentiation and higher levels of specific IgG antibodies.
“The good news is that prolonged inflammation seen in these patients reverted to healthy levels within two years after initial infection,” said Fong, who added that the study also provided much-needed insights on lingering effects experienced by high-risk patients who often had comorbidities like diabetes or high blood pressure.
“We believe our study offers some reassurance to affected individuals that their symptoms will resolve with time,” said Fong. “Hopefully, our findings will also accelerate the search for treatments that aid recovery from long COVID. Further studies are needed to identify the mechanisms behind the prolonged inflammation and immune activation caused by COVID-19.”
The A*STAR-affiliated researchers contributing to this research are from the A*STAR Infectious Diseases Labs (ID Labs) and the Singapore Immunology Network (SIgN).
