INTRODUCTION
Long Covid has forced clinicians to move beyond symptom based frameworks and confront a condition driven by immune instability, heterogeneity, and incomplete recovery. As evidence has accumulated around immune dysregulation, viral persistence, endothelial injury, and autoimmune phenomena, monoclonal antibodies and targeted immunotherapies have increasingly entered clinical and research discussions.The key question is no longer whether immunotherapy is biologically plausible, but which agents might be relevant, in which biological subgroups, and where evidence currently stops.
Why Immunotherapy Is Being Explored in Long Covid
Multiple studies have described persistent immune activation in Long Covid, including altered T cell phenotypes, abnormal B cell responses, autoantibody production, endothelial inflammation, and impaired viral immune control. These findings mirror mechanisms seen in autoimmune disease, chronic inflammatory syndromes, and post viral conditions.
Monoclonal antibodies offer targeted intervention against specific immune pathways. In theory, this precision could be valuable in a condition as complex as Long Covid. In practice, the absence of validated biomarkers makes patient selection the central challenge.
Antiviral Monoclonal Antibodies and Viral Persistence
Early interest focused on antiviral monoclonal antibodies originally developed for acute SARS CoV 2 infection, including casirivimab imdevimab (REGN COV2), sotrovimab, tixagevimab cilgavimab (Evusheld), and bebtelovimab.
The hypothesis was that persistent viral fragments or low level reservoirs might continue to stimulate the immune system in some patients. A small number of observational reports described symptom improvement when antiviral therapies were given months after infection. However, controlled data remain limited, and viral evolution has significantly reduced the neutralising activity of several early monoclonals.
At present, antiviral monoclonal antibodies are not supported as routine treatment for Long Covid, although viral persistence remains an active area of investigation.
B Cell Depletion and Autoimmune Mechanisms
Autoantibodies targeting autonomic receptors, endothelial structures, and neural antigens have been reported in Long Covid cohorts. This has led to interest in B cell directed therapies, particularly rituximab, a CD20 targeting monoclonal antibody widely used in rheumatology and neurology.
Rituximab has theoretical appeal in patients with immune mediated phenotypes, as it reduces B cell driven autoantibody production. However, evidence in Long Covid is inconsistent. Some patients report improvement, while others experience no benefit or deterioration.
A major concern is Epstein Barr virus latency. EBV resides in B cells, and B cell depletion may disrupt immune control of latent infection. This may explain why some individuals worsen following rituximab, developing increased fatigue, cognitive dysfunction, or immune instability.
At present, rituximab cannot be recommended outside of research settings for Long Covid, but it remains an important mechanistic probe into disease biology.
Cytokine Targeting and Systemic Inflammation
Interleukin 6 has been implicated in acute Covid and post acute inflammatory responses. This has prompted interest in IL 6 receptor antagonists such as tocilizumab and sarilumab, as well as other cytokine targeted therapies including anakinra, an IL 1 receptor antagonist.
In Long Covid, however, inflammation is often low grade, fluctuating, and poorly captured by routine biomarkers. Clinical experience suggests that cytokine blockade may benefit a small subgroup with persistent inflammatory signatures, but offers little benefit for those whose symptoms are driven primarily by autonomic dysfunction or impaired energy metabolism.
Broad immune suppression in the absence of clear inflammatory drivers carries significant risk and uncertain benefit.
Endothelial Dysfunction and Immunomodulation
Endothelial injury and microvascular dysfunction have been described in Long Covid, particularly in patients with exertional intolerance, dysautonomia, and post exertional symptom exacerbation. Experimental interest has included immunomodulatory agents such as intravenous immunoglobulin (IVIG) and complement pathway inhibitors, although data remain sparse.
IVIG has been trialled in small cohorts, particularly in patients with overlapping autoimmune or neuropathic features. While some report functional improvement, others show no response, and controlled trials are lacking.
Mast Cell Activation, EBV Reactivation, and Immune Feedback Loops
An emerging area of interest involves mast cell activation and latent virus reactivation, particularly Epstein Barr virus. Elevated EBV early antigen antibodies have been reported in Long Covid cohorts, suggesting impaired immune control rather than acute infection.
Mast cells interact closely with the immune and autonomic nervous systems. Symptoms commonly reported in Long Covid such as flushing, tachycardia, gastrointestinal disturbance, hypersensitivity reactions, cognitive dysfunction, and orthostatic intolerance overlap with mast cell activation phenotypes.
No monoclonal antibody has demonstrated proven efficacy for mast cell driven Long Covid. Agents such as omalizumab, an anti IgE monoclonal antibody used in allergic disease, have been discussed hypothetically, but evidence remains anecdotal and insufficient for recommendation.
What Has Been Trialled and Where Evidence Ends
Monoclonal antibodies explored in relation to Long Covid include antiviral agents such as sotrovimab and tixagevimab cilgavimab, immune modulators such as rituximab, cytokine inhibitors including tocilizumab and anakinra, and immunomodulatory therapies such as IVIG.
Across studies, outcomes are inconsistent. Some patients improve, many do not, and some worsen. This variability almost certainly reflects underlying biological heterogeneity rather than simple treatment failure.
Without validated biomarkers, longitudinal functional endpoints, and stratified trial design, interpretation remains limited.
Ongoing Research Including Work by Klimas and Others
Current research is actively exploring whether monoclonal antibodies may have a role in selected Long Covid patients. Work led by Nancy Klimas and collaborators is investigating agents such as sipavibart, a long acting monoclonal antibody targeting SARS CoV 2 spike protein. Early clinical observations and case reports have suggested that some patients may experience significant improvement following monoclonal antibody infusion, raising the possibility that persistent viral fragments or ongoing immune stimulation may be relevant in a subset of cases.
However, more rigorous studies have shown mixed results, with some trials failing to demonstrate clear benefit across broader patient groups. This reinforces a central challenge in Long Covid research: therapies that appear effective in individual cases may not generalise without careful biological stratification.
Cost, Risk, and Clinical Responsibility
Monoclonal antibodies are costly, resource intensive, and associated with non trivial risks including infection, immune suppression, and paradoxical symptom exacerbation. In a condition with uncertain trajectory, escalation of therapy must be justified by more than theoretical plausibility.
For clinicians, restraint is not therapeutic nihilism. It is responsible medicine.
Who Might Benefit and Who Likely Will Not
Patients with clear immune mediated phenotypes, documented autoimmunity, or persistent inflammatory markers may be more likely to benefit from targeted immunotherapy. Those with predominant autonomic instability, post exertional symptom exacerbation, or metabolic dysfunction appear less likely to respond and may be harmed by immune suppression.
Until reliable stratification tools exist, treatment selection remains speculative.
What Clinicians Need Next
Long Covid challenges existing immunological models. It exposes the limits of diagnosis driven medicine and highlights the need for functional, longitudinal, and biologically stratified approaches.
Monoclonal antibodies may eventually have a role, but only when matched to mechanism, timing, and patient biology. Until then, their primary value lies in research rather than routine clinical care.
Frequently Asked Questions
Can monoclonal antibodies treat Long Covid directly
At present, there is no monoclonal antibody that is proven to treat Long Covid as a single condition. The challenge is that Long Covid is not one disease but a collection of overlapping biological processes. Monoclonal antibodies target specific pathways, and without identifying which pathway is driving symptoms in a given patient, treatment remains imprecise.
Why do some patients report improvement after monoclonal antibody treatment
Improvement likely reflects alignment between the therapy and the dominant mechanism in that individual. For example, if a patient’s symptoms are driven by persistent immune activation or autoantibodies, a targeted therapy may produce benefit. If symptoms are driven by autonomic dysfunction or metabolic impairment, the same therapy may have little effect.
Is viral persistence still a valid explanation for Long Covid symptoms
There is ongoing evidence suggesting that viral fragments or reservoirs may persist in some individuals, particularly in tissues such as the gut. However, this is not universal. Long Covid likely includes both persistence-driven and non-persistence-driven subtypes, which is why antiviral monoclonal antibodies show inconsistent results.
Why has rituximab not shown consistent benefit in Long Covid
Rituximab depletes B cells, which may reduce autoantibody production. However, B cells also play a role in immune regulation and viral control. In some patients, removing B cells may destabilise immune balance or allow latent viruses such as Epstein Barr virus to reactivate, leading to worsening symptoms.
Can monoclonal antibodies make Long Covid worse
Yes, in some cases. Immune modulation can have unintended effects, particularly in a system that is already unstable. Suppressing one pathway may amplify another. For example, reducing immune surveillance could worsen viral reactivation or alter inflammatory signalling in unpredictable ways.
Why are inflammatory markers often normal if immune therapies are being considered
Standard inflammatory markers such as CRP or ESR are not sensitive enough to detect low-grade or compartmentalised inflammation. Long Covid often involves subtle immune dysregulation rather than overt systemic inflammation, which is why routine tests can appear normal despite significant symptoms.
Is there a subgroup of patients more likely to benefit from immunotherapy
Patients with clear evidence of immune-mediated pathology, such as autoantibodies, persistent inflammatory markers, or overlap with recognised autoimmune disease, are more plausible candidates. However, even within this group, response is variable and not yet predictable.
Why are monoclonal antibodies not widely used for Long Covid despite biological plausibility
The main limitation is lack of stratified evidence. Most studies are small, uncontrolled, or observational. Without biomarkers to identify responders and non-responders, widespread use would expose many patients to risk without clear benefit.
How does Long Covid differ from classical autoimmune disease in this context
While there is overlap, Long Covid often involves fluctuating, multi-system dysregulation rather than stable, organ-specific autoimmune patterns. This makes targeted immunotherapy more difficult, as the underlying drivers may shift over time.
What is the biggest barrier to progress in this area
The absence of validated biomarkers and patient stratification. Without being able to define biological subtypes, treatments remain trial-and-error. Progress depends on linking symptoms to measurable mechanisms and designing trials around those subgroups.
Disclaimer
This article is for educational and discussion purposes only and does not constitute medical advice. Treatment decisions should be made within appropriate clinical and research frameworks.