It’s not unusual to feel fatigued or experience brain fog after recovering from a viral illness. The body has just expended significant energy fighting off an infection, and a temporary dip in energy or mood is understandable.
But for some people, these symptoms linger or deepen into something more serious: post-viral depression.
A recent study by researchers from the US biotech company Tuning Fork suggests that at least some cases of post-viral depression in people recovering from COVID-19 may have measurable biological underpinnings.
Company CEO Yuichi Hikichi and fellow researcher Kohei Kunieda profiled immune activity through saliva taken from volunteers at the height of the pandemic; specifically, they measured immunoglobulin A (IgA), an antibody commonly found in mucosal secretions, to identify patterns that might distinguish people with post-COVID depression from those without it.
Hikichi and Kunieda identified distinct immune-linked signatures in people with post-viral depression. “This suggests that at least a subset of post-viral depression may have detectable biological features, beyond symptom-based descriptions alone,” he said.
These findings point to the possibility that depression following viral illness may, in some cases, be associated with immune-related changes that persist after the infection has resolved.
Depression is typically diagnosed based on reported symptoms and clinical evaluation, which can vary widely between patients. Objective biomarkers, if validated, could provide a more standardized way to identify and classify certain subtypes of the condition.
“For clinicians, such markers could complement symptom-based assessments, while for patients – especially those who struggle to clearly articulate their symptoms – objective indicators may help validate their experience,” Hikichi said.
At the same time, the study raises broader questions about whether these immune patterns are unique to COVID-19 or reflect a more general phenomenon seen after other viral infections.
“At this stage, it is difficult to determine whether the immune signatures we observed are specific to SARS-CoV-2,” Hikichi explained. “To answer that definitively, similar protein microarray analyses would need to be performed under comparable conditions in individuals recovering from other viral infections.”
He added that some of the antibody targets identified in the study are involved in cellular stress responses and viral processes used by pathogens such as influenza, suggesting that similar mechanisms could be at play across different infections.
Outside experts say the study contributes to an evolving understanding of post-viral neuropsychiatric conditions, emphasizing that such conditions have long been underrecognized.
“Similar to depression, chronic fatigue and disability due to brain fog has been dismissed and discounted as ‘neurotic’ or ‘functional’ and only now with the advances in biomarkers of the disease, we start understanding the origins of post-viral neuro-psychiatric disorders, including depression as causing real suffering and disability, but also points out to novel treatment options like anti-viral or immune therapies to treat them,” says Helen Lavretsky, who was not affiliated with the study. Lavretsky is the director of the Post-COVID Psychiatry Clinic at the University of California, Los Angeles.
Lavretsky also notes that post-COVID depression shares features with other post-viral syndromes, including fatigue and mood disturbances. The scale of the COVID-19 pandemic has brought unprecedented attention to post-viral conditions, with an estimated 10% to 30% of infected individuals developing neuropsychiatric symptoms, she explained.
This has created an urgent need for clinicians to better understand underlying mechanisms and consider a broader range of treatment approaches, including antiviral and immunomodulatory therapies alongside standard antidepressants, according to Lavretsky.
Lavretsky notes that while the presence of certain antibodies correlates with depressive symptoms, it remains unclear whether they play a direct causal role or simply reflect broader immune dysregulation.
“The key limitation is that this kind of study shows an association,” she says. “It does not prove the antibodies caused the depressive symptoms. They could be a marker of the underlying immune process instead.”
Looking ahead, Hikichi emphasizes that the findings are preliminary and limited to one class of antibodies. Larger studies incorporating additional immune markers will be needed to determine whether these signatures can move beyond descriptive biomarkers to help clarify disease mechanisms and guide treatment.
If successful, this work could mark an important step toward more personalized approaches to diagnosing and managing depression in the aftermath of viral illness.
This study has been published in Scientific Reports.
Fact-checked by Mike McRae
