Supporting Immune Resilience in Modern Times

Supporting Immune Resilience in Modern Times

Author: Min Geraets | BNatMed | Naturopath & Medical Herbalist 

Originally published in the Avena journal of the New Zealand Association of Medical Herbalists (NZAMH).

The global Covid-19 pandemic reshaped the clinical landscape and scientific understanding of immune function.  Many practitioners now report an increasing number of clients presenting with altered immune patterns following viral infection.  These may include recurrent infections, persistent fatigue, chronic inflammation, immune hypersensitivity and prolonged recovery from illness. 

Emerging research suggests that viral infections can leave lasting imprints on immune physiology, inflammatory regulation and microbiome composition.  Rather than returning immediately to pre-infection baseline, immune responses may remain altered for extended periods.1

These findings reinforce a core belief within naturopathic medicine; that immune health extends far beyond pathogen defence.  It reflects the overall state of the body’s internal terrain, including mucosal barrier integrity, microbial ecology, nervous system balance, metabolic health and environmental exposures.

This Phytobrief explores the evidence on immune regulation arising in the post-Covid-19 era.  It has a particular focus on immune training, mucosal immunity, the microbiome-immune axis and neuroimmune regulation.  It also looks at practical clinical strategies for supporting immune resilience in clinical practice.

The immune system as a dynamic ecosystem 

The immune system is divided into two broad components: innate immunity and adaptive immunity.  Innate immunity is the first line of defence and is characterised by a rapid, non-specific response to invading pathogens.  It includes physical and chemical barriers, such as the skin, mucous membranes and saliva, as well as immune cells including macrophages, neutrophils, basophils, and mast cells.  These components are ‘ready to act’ and provide immediate protection during the initial stages of infection.2

Adaptive immunity is the second line of defence and is characterised by an antigen-specific response and the development of immunological memory.  This allows the immune system to mount a stronger and more specific response upon subsequent encounters with the same pathogen.  Adaptive immunity includes antibodies, which target foreign pathogens in the bloodstream, and T cells, which recognise pathogens that have infected host cells.  T cells can directly eliminate infected cells or help regulate and support the antibody response.2

Immune responses are influenced by nutrition, microbial diversity, psychological stress, sleep patterns, environmental toxins and previous infections.3  These factors continuously interact to shape immune reactivity and tolerance.

A key concept emerging in recent years is trained immunity.  Unlike classical immunological memory, which is mediated by adaptive immune cells such as T and B lymphocytes, trained immunity refers to long-term functional changes in innate immune cells.  Following exposure to specific immunomodulators, innate immune cells such as monocytes, macrophages and NK cells, undergo epigenetic and metabolic reprogramming.  This alters their responsiveness to subsequent infections, either enhancing or dampening inflammatory responses.4

This phenomenon may partly explain why previous infections influence susceptibility to future illness and why immune responses vary widely between individuals.  Clinically, this reinforces the importance of assessing immune terrain rather than focusing solely on acute infection management.

Post-viral immune dysregulation 

Persistent symptoms and unexplained chronic disability following viral infections are not a new phenomenon.  Post-viral syndromes have been described following influenza, Epstein–Barr virus and other infectious diseases.5  The extraordinary scale of the Covid-19 pandemic, however, has attracted widespread attention to the potential long-term effects of viral illness.

A subset of infected individuals, experience persistent symptoms weeks or months after the initial infection, a condition commonly referred to as Long Covid or post-acute sequelae of SARS-CoV-2 infection (PASC).6 

Symptoms may include:

  • Chronic fatigue
  • Cognitive impairment
  • Dysautonomia
  • Breathlessness
  • Musculoskeletal pain
  • Recurrent infections.

Several mechanisms are currently proposed to explain post-viral immune dysregulation.

Persistent inflammatory signalling 

Elevated levels of pro-inflammatory cytokines, including IL-6, TNF-α and interferons, have been observed in some individuals following viral infections.7  These inflammatory mediators may contribute to ongoing fatigue, shortness of breath, cognitive impairment and tissue inflammation.

Viral antigen persistence 

In certain cases, viral RNA fragments or proteins may remain within tissues long after acute infection has resolved.  Emerging evidence suggests that components of SARS-CoV-2 can persist for months after infection in ACE2-expressing cells in the lungs, small intestine and nasopharynx.8  This persistent antigen exposure may continue to stimulate immune responses.

Immune exhaustion 

Prolonged immune activation can lead to functional exhaustion of immune cells, particularly T cells.  Exhausted T cells exhibit reduced antiviral activity and impaired immune regulation.9  Clinically, this may manifest as increased susceptibility to subsequent infections.

Autoimmune mechanisms 

Molecular mimicry between viral proteins and host tissues may trigger autoimmune reactions. Autoantibodies have been detected following certain viral infections, including Covid-19.  Neurological symptoms post-Covid-19 are suspected to originate from a dysregulated immune response with autoantibody involvement.10  While research in this area remains ongoing, these mechanisms highlight the complexity of immune recovery following viral illness.

Mucosal immunity: The first line of defence 

A significant proportion of immune activity occurs at mucosal surfaces, including the oral cavity and the respiratory, genitourinary and gastrointestinal tracts.  These tissues represent the primary interface between the body and the external environment.11

Mucosal immunity relies heavily on secretory immunoglobulin A (sIgA), the predominant antibody found in mucosal secretions.  Secretory IgA plays a crucial role in immune defence by binding pathogens and toxins while maintaining tolerance toward beneficial microbes and food antigens.  Unlike many immune responses, sIgA activity generally occurs without triggering significant inflammation.  This allows mucosal surfaces to remain protected while preserving tissue integrity.12

Reduced sIgA levels are associated with increased susceptibility to respiratory infections, gastrointestinal disturbances and allergic disease.13  Psychological stress, viral infections and nutritional deficiencies can all reduce sIgA production.  Supporting mucosal immunity is a key strategy for enhancing immune resilience.

The microbiome-immune axis

The human microbiome has emerged as one of the most important regulators of immune function.  Microbial communities interact closely with immune cells, influencing immune tolerance, inflammatory signalling and pathogen resistance.14 

The gastrointestinal microbiome plays a particularly important role in immune regulation.  Commensal bacteria produce metabolites such as short-chain fatty acids (SCFAs), including butyrate, acetate and propionate.  These metabolites influence regulatory T-cell development, epithelial barrier integrity and anti-inflammatory signalling pathways.15

Disruption of microbial balance, known as dysbiosis, may contribute to immune dysfunction through several mechanisms:

  • Increased intestinal permeability
  • Chronic low-grade inflammation
  • Reduced regulatory immune signalling 
  • Impaired antiviral defence.16

Recent studies investigating individuals recovering from Covid-19 have reported alterations in gut microbiota composition, including reductions in beneficial bacterial species such as Faecalibacterium and Eubacterium and an increase in the abundance of harmful bacterial species like Enterobacteriaceae.  These microbial shifts have been associated with increased inflammatory markers, endothelial dysfunction and more severe disease outcomes.17  This evidence highlights the importance of microbiome support in post-viral recovery protocols.

The gut-lung axis

The gut–lung axis describes the bidirectional relationship between gastrointestinal microbiota and respiratory immune function.  Microbial metabolites produced in the gut can influence immune responses in the lungs via systemic circulation and immune cell signalling.  SCFAs help regulate immune cell activity within respiratory tissues, promoting balanced inflammatory responses during infection.18

Conversely, intestinal dysbiosis may impair respiratory immunity and increase susceptibility to respiratory pathogens.  This interaction may explain why gastrointestinal symptoms often accompany respiratory infections and why individuals with metabolic or digestive disorders may experience more severe respiratory illness.  Supporting gut health may therefore contribute to enhanced respiratory immune resilience.

Neuroimmune regulation

The immune system is closely connected with the nervous and endocrine systems.  Psychological stress, emotional trauma and sleep disruption can significantly influence immune activity and increase risk of infection.

The hypothalamic–pituitary–adrenal (HPA) axis regulates cortisol production in response to stress.  Acute cortisol release helps regulate inflammation, but chronic stress can suppress immune function.19

Chronic stress has been associated with:

  • Reduced natural killer cell activity
  • Lower secretory IgA levels
  • Increased susceptibility to viral infections
  • Altered inflammatory cytokine production.19

The autonomic nervous system also influences immune regulation through vagal signalling pathways.  The vagus nerve participates in the cholinergic anti-inflammatory pathway, which modulates cytokine production and inflammatory responses.20  Reduced vagal tone has been associated with increased systemic inflammation.  For clients experiencing chronic stress or burnout, supporting nervous system regulation is an important component of immune recovery.

Nutritional influences on immune resilience 

Adequate nutritional status is vital for healthy immune system functioning.  Several micronutrients play critical roles in immune cell development, inflammatory regulation and antiviral defence.

Vitamin D (1000-4000 IU/day)

Vitamin D influences both innate and adaptive immunity.  It promotes antimicrobial peptide production and helps regulate inflammatory responses.21  Low vitamin D status has been associated with increased susceptibility to respiratory infections.

Zinc (10-75 mg/day)

Zinc is essential for immune cell development, antiviral and antioxidant activity and cytokine regulation. 22  Zinc deficiency impairs both innate and adaptive immune responses.  

Vitamin C (250-2000 mg/day)

Vitamin C functions as an antioxidant and supports leukocyte function, epithelial barrier integrity and immune signalling.  Adequate vitamin C intake may reduce the duration and severity of respiratory infections.  Prophylactic prevention of infection requires lower dosing (250 mg/day), while treatment of acute infections requires higher dosing (1-2g/day) to compensate for the increased inflammatory response and metabolic demands.23  Vitamin C is not stored in the body and therefore lacks a long-term reservoir.  For this reason, consistent daily intake from dietary sources, and supplements when appropriate, are necessary.

Selenium (100-300 µg/day)

Selenium contributes to antioxidant defence through its role in glutathione peroxidase enzymes and immune cell regulation.24  Low selenium status has been associated with increased viral virulence and impaired immune function. 

N-acetyl-cysteine (NAC) (600-1200 mg/day)

NAC is a precursor to the body’s primary endogenous antioxidant, glutathione.  It functions as an immunomodulatory compound with indirect antiviral activity and the ability to reduce pro-inflammatory cytokines.25  Its mucolytic, antioxidant, anti-inflammatory, and antiviral properties contribute to its clinical benefits in the treatment of respiratory diseases.

Pre, pro and post-biotics 

Prebiotics, probiotics, and postbiotics support immune health primarily by influencing the gut microbiota and its interaction with the immune system.

  • Prebiotics are non-digestible dietary components that serve as food for beneficial gut bacteria, selectively stimulating their growth and activity.  This process promotes the production of metabolites such as SCFAs, which help regulate immune responses, strengthen the intestinal barrier and maintain a balanced gut microbiome.26
  • Probiotics are live beneficial microorganisms that can modify the composition of the gut microbiota, compete with pathogens, enhance intestinal barrier function, and modulate immune signalling pathways.  Through these mechanisms, they help support immune system maturation and reduce inflammation.26
  • Postbiotics are bioactive compounds produced by probiotics during their metabolism, including microbial cell components, peptides and SCFAs.  These substances can exert immunomodulatory and anti-inflammatory effects, contributing to gut barrier integrity and supporting overall immune health without the presence of live microbes.26

Herbal medicine and immunomodulation 

Herbal medicine offers a diverse range of bioactive compounds that support immune regulation rather than simply stimulating immune responses.  The multiple therapeutic actions of medicinal plants enable a tailored approach to modern immune support, allowing practitioners to address the varied needs of clients living in a post-pandemic world.

Adaptogens for post-viral recovery 

  • Siberian Ginseng (Eleutherococcus senticosus) acts as both an adaptogen and immunomodulator, enhancing resilience during recovery from prolonged illness.  It supports mitochondrial function, improves endurance and reduces stress-induced immune suppression.27,28  Clinically, Siberian ginseng is well-suited to individuals presenting with post-viral fatigue, low vitality and increased susceptibility to recurrent infections.
  • Withania (Withania somnifera) plays a central role in post-viral recovery where fatigue, sleep disturbance and nervous system dysregulation are present.  Its withanolides exert immunomodulatory effects through regulation of cytokine activity and enhancement of NK function.29,30  Withania also modulates the stress response via the HPA axis, making it particularly relevant in cases where immune dysfunction is compounded by chronic stress or burnout.  Emerging research is exploring its potential applications for Long-Covid presentations characterised by fatigue, sleep disturbances and cognitive impairement.31

Antivirals 

  • Baical skullcap (Scutellaria baicalensis) exerts antiviral effects primarily through its key constituents, baicalein and baicalin.  In pre-clinical studies, these actives have demonstrated antiviral activity against SARS-CoV-2 and have been shown to inhibit virus-induced cellular injury.  Baical skullcap offers additional anti-inflammatory, antioxidant and neuroprotective benefits, making it useful in presentations involving neuroinflammation or post-viral cognitive impairement.32
  • Elderberry (Sambucus nigra) is widely used in acute viral infections, where it inhibits viral replication and support cytokine-mediated defence.  Its flavonoids interfere with viral entry and replication, particularly in influenza viruses.33
  • Kānuka (Kunzea ericoides) is a New Zealand native that has been traditionally used in respiratory infections.  Preliminary evidence has demonstrated antiviral and antimicrobial activity attributed to its acyl phloroglucinol constituents.34
  • Nigella (Nigella sativa) exhibits antiviral, anti-inflammatory and immunomodulatory effects.  Nigella's key constituents, flavonoids, phenolics and thymoquinone, have demonstrated potential antiviral activity against virus progression and replication (including SARS-CoV-2) in pre-clinical and early clinical studies.  Nigella has been shown to enhance NK cell activity, modulate T-cell responses and reduce inflammatory markers including TNF-α and CRP.  These multi-faceted properties make Nigella particularly relevant in post-viral states where there is chronic low-grade inflammation and immune dysregulation.35

Immunomodulation 

  • Andrographis (Andrographis paniculata) exerts immunomodulatory and anti-inflammatory effects, largely attributed to its diterpenoid constituent, andrographolide to modulate cytokine production by inhibiting pro-inflammatory mediators including IL-6 and TNF-α, while supporting T-cell activity.  Clinically, it bridges acute and post-acute phases, particularly where lingering inflammation or recurrent respiratory symptoms presist.36
  • Astragalus (Astragalus membranaceus) is commonly used to restore immune competence.  Its polysaccharides enhance macrophage activity, support interferon production and promote T- and B-cell proliferation, thus strengthening both innate and adaptive immunity.37
  • Cat's claw (Uncaria tomentosa) exhibits immunomodulatory activity primarily by downregulating pro-inflammatory pathways, reducing IL-6 levels and inhibiting activation of NF-κB, which are drivers of inflammatory gene expression.38  Cat's claw is well-suited to individuals presenting with ongoing inflammatory symptoms, joint pain or immune overactivation.
  • Echinacea (Echinacea spp.) remains one of the most versatile immunomodulators in Western herbal medicine.39  It exhibits immunomodulatory effects through a proposed multi-target mechanism, primarily mediated by alkylamides that interact with cannabinoid receptor 2 (CB2) and modulate toll-receptor 4 (TLR4) signalling.  Leading to reduced pro-inflammatory cytokines including TNF- and IL-6, while rebalancing Th1/Th2 immune responses.40  Echinacea's context-dependent immunomodulation makes it highly relevant for immune dysregulation. 
  • Reishi (Ganoderma lucidum) offers a unique combination of immunomodulatory, anti-inflammatory and adaptogenic properties.  Its polysaccharides, particularly β-D-glucans stimulate macrophage phagocytosis, promote dendritic cell maturation and support T and B cell proliferation.  Reishi's triterpenoids regulate inflammatory pathways by modulating NF-κB and MAPK signalling.41  Reishi is valuable in chronic immune dysregulation, autoimmunity and post-viral fatigue, where both immunomodulation and nervous system support are required.

Lifestyle foundations for immune health 

Lifestyle interventions remain fundamental to immune resilience.

  • Adequate sleep and rest: Restorative sleep works to regulate the immune system and promotes the release of anti-inflammatory mediators.  Sleep deprivation is associated with increased susceptibility to infection.42
  • Physical activity: Moderate physical activity supports immunity by increasing immune surveillance, promoting beneficial remodelling of the immune system and reducing chronic inflammation.  These effects improve immune responses to vaccines and are associated with lower risks of infection, severe illness and mortality from diseases including Covid-19.43 
  • Social connection: Psychosocial factors cannot be overlooked when it comes to supporting immune health.  Research suggests that loneliness and social isolation may increase inflammatory signalling and reduce immune resilience.44

Clinical assessment: Evaluating immune terrain 

Incorporating immune assessment into consultations allows practitioners to identify patterns of immune dysregulation.

Suggested case history questions

  • How frequently do you experience infections?
  • How long does it typically take you to recover?
  • Do you experience fatigue after illness?
  • Have you had Covid-19 or other significant viral infections?
  • Do you experience digestive disturbances or food sensitivities? 
  • How would you describe your stress levels and sleep quality?

Clinical observations

  • Signs of chronic inflammation (persistent fatigue, body aches, joint stiffness, skin rashes, sinus congestion)
  • Alterations to digestion (diarrhoea, constipation, bloating, flatulence)
  • Enlarged lymph nodes
  • Nutritional deficiencies.

Possible clinical patterns

  • Post-viral inflammatory syndrome
  • Immune exhaustion pattern 
  • Microbiome-driven immune dysregulation
  • Stress-mediated immune suppression.

Key takeaways 

  • Immune care has evolved: The immune system functions as a dynamic ecosystem shaped by microbial, metabolic and neurological influences.  Effective immune support therefore extends beyond pathogen defence to include restoration of systemic balance.
  • Post-viral immune disruption is increasingly recognised: Viral infections may leave lasting effects on immune signalling, inflammation and microbial balance.  Practitioners are increasingly encountering clients presenting with prolonged fatigue, inflammatory symptoms and altered immune responsiveness following infection.
  • Mucosal immunity is central: Secretory IgA and mucosal barrier integrity are critical for pathogen defence and immune tolerance.  Supporting mucosal health is a key strategy for reducing susceptibility to infection and restoring immune balance.
  • The microbiome regulates immune function: Gut microbial health influences systemic inflammation and respiratory immunity through the gut-lung axis.  Restoring microbiome balance is an important component of post-viral recovery.
  • Stress profoundly affects immunity: Chronic stress can supress immune responses and alter inflammatory regulation.  Addressing stress physiology and supporting autonomic balance are essential aspects of modern immune care.
  • A terrain-based approach improves outcomes: Combining nutritional support, herbal immunomodulation, microbiome restoration and lifestyle interventions allows practitioners to address the underlying terrain that shapes immune responses.  Practitioners are well positioned to guide post-pandemic immune care due to the individualised approach inherent to herbal prescribing. 

A clinical framework for immune restoration

Clinical presentation

Key characteristics

Therapeutic goals

Nutritional strategies

Herbal support

Lifestyle & adjunctive therapies

Acute viral infection support

Early infection phase; fever, sore throat, respiratory symptoms, fatigue, body aches.

Support innate immune responses; reduce viral replication; moderate excessive inflammation; maintain hydration and nutrient status.

Vitamin C (1-2g/day), zinc (75mg/day, in divided doses), adequate protein intake, hydration with electrolyte support, warming broths and soups.

Andrographis paniculata, Astragalus membranaceus Echinacea spp., Kunzea ericoides, Nigella sativa, Sambucus nigra, Scutellaria baicalensis. These herbs support antiviral activity, immune activation and inflammatory balance.

Rest and sleep optimisation; gentle warmth; steam inhalation with antimicrobial essential oils; nutrient-dense meals.

Post-viral fatigue

Persistent fatigue, brain fog, low stamina, dysautonomia, fluctuating immune resilience. Often follows viral illness including Covid-19.

Reduce chronic inflammation; support mitochondrial function and energy production; restore immune regulation; support nervous system recovery.

Anti-inflammatory diet rich in omega-3 fatty acids, polyphenols and antioxidants; magnesium; B-complex vitamins; CoQ10; adequate protein intake to support tissue repair.

Adaptogens such as Withania somnifera and Eleutherococcus senticosus; mitochondrial-support herbs such as Panax ginseng; nervines such as Scutellaria lateriflora.

Gradual pacing of activity (‘energy envelope’ approach); sleep restoration; gentle movement such as walking or restorative yoga; breathwork and vagal tone practices.

Immune dysregulation

Frequent colds or respiratory infections; slow recovery from illness; low mucosal immunity; possible microbiome imbalance.

Restore mucosal immunity; improve microbiome diversity; enhance immune surveillance while maintaining tolerance.

Fibre-rich whole-food diet; fermented foods; prebiotic fibres; vitamin D, zinc and selenium repletion where indicated.

Astragalus membranaceus, Echinacea spp., Ganoderma lucidum. These herbs support immune modulation and resilience.

Sleep optimisation; moderate physical activity; sunlight exposure; stress reduction practices; microbiome restoration strategies.

Chronic inflammatory immune state

Persistent low-grade inflammation; autoimmune tendencies; systemic symptoms such as joint pain, brain fog or metabolic dysfunction.

Reduce inflammatory signaling; support regulatory immune pathways; improve gut barrier integrity; address metabolic contributors.

Anti-inflammatory dietary pattern (Mediterranean-style); omega-3 fatty acids; polyphenol-rich foods (berries, green tea, herbs); reduction of ultra-processed foods.

Anti-inflammatory herbs including Curcuma longa, Echinacea spp., Scutellaria baicalensis and Glycyrrhiza glabra.

Stress reduction; sleep restoration; gut healing protocols; mindfulness or meditation practices.

 

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