Gut Microbiota, Immunoglobulin A, and Vaccine Efficacy

The gut microbiota has recently been recognized as an important factor affecting the efficacy of vaccines. One protein that has received attention is immunoglobulin A (IgA), which is crucial for maintaining a healthy balance of microbes and confining them to the mucosal surface of the gut. Studies have shown that low levels of IgA or deficiency of IgA can disrupt the normal gut microbiota and result in a microbial profile that impairs vaccine responses. Clinicians and health systems worldwide need to be aware of the relationship between IgA, gut microbes, and vaccine response, including identifying nonresponders, diagnosing the cause, and vaccinating individuals with low levels of IgA who are at high risk of vaccine-preventable diseases.

Why It Matters

Vaccines have proven to be lifesavers by preventing disease and severe illness. However, it is well established that full and long lasting vaccine-induced immunity is not achieved in all individuals. Significant numbers of individuals do not make an adequate immune response to multiple vaccines, or loose that response prematurely. This results in repeated infections in vaccinated individuals as well as fewer than optimal levels of antibody following completion of the standard vaccine series. This leads to cases of serious vaccine-preventable disease in vulnerable individuals. Outbreaks and increased acute care visits, hospitalizations, lost productivity and long term sequelae further place a burden on our health care system.

The gut is one of the body’s largest immune organs where immune cells are constantly primed to fight invading pathogens. Immune cells in the gut such as T cells and B cells interact with the tissue of the intestine as they survey for pathogens, food, commensal microbes and microbial products. To achieve long lasting vaccine-induced immunity several steps must occur efficiently including antigen recognition, immune cell activation, generation of long lived memory cells and production of long lasting antibodies. However, chronic inflammation or altered microbial signals in the gut can reroute the immune response away from optimal vaccine antigen-specific immunity.

How IgA supports healthy vaccine responses

IgA is the most abundant antibody at mucosal surfaces throughout the body and has been referred to as the “peacekeeper” of the gut for its role in preserving homeostasis by preventing overgrowth of commensal organisms. In addition to neutralizing and killing pathogens, IgA coats commensal organisms and may prevent excessive adherence to intestinal mucosa and also limit their ability to transmigrate into tissue where they could induce inflammation. Once IgA functions are compromised, organisms can overgrow, change in species prevalence or pathogenicity and transmigrate more extensively to the surface of the gut lumen. The result is the generation of sustained low-grade immune activation.

Vaccines are unlikely to perform optimally in settings with chronic immune activation because the immune responses elicited by the pathogen can become ‘exhausted’ and also diverted away from the vaccine antigen. Activation of immune pathways also requires counter-regulatory signals to control excessive immune activation, which over the long term can lead to production of a less responsive, less coordinated or less effective immune system that is unable to mount a vigorous or ‘memory’ immune response to vaccine antigens.

Why the microbiota matters even without IgA deficiency

Variation in IgA levels may be influenced by a host of factors that result in microbialuta disruption, the many possible causes of which were described in the prior section. Here we note that besides environmental toxins and antibiotic usage, GI infections, chronic stress, malnutrition, obesity, inflammatory bowel disease and other medical treatments with immune-modulating effects all can perturb the gut microbial community and thus cause changes in the training signals provided to the immune system. For this reason, some vaccines— particularly those requiring optimal levels of specific antibodies for adequate efficacy—may be less effective in individuals with immune system dysfunction.

Timing is everything in understanding how timing impacts the shape of the gut immune environment. The microbiota dynamics can shift in days, and by the time you notice a microbial pattern, it may have changed because of antibiotics, illness, travel or a new diet. It’s a moving target. Interestingly, the two patients in the study were only 7 years old and of relatively good health, yet their microbiome responses to different schedules already failed to mirror each other.

Clinical stakes and system-level consequences

A particular focus will be on those populations for whom a decrease in vaccine efficacy would have the greatest impact. These individuals are elderly and/or are immunocompromised, having a reduced response to vaccination for many vaccines. In addition to the less than optimal immune response to vaccination, their mucosal immune response and mucosal imbalance as well as their alterations in resident microbiota could further compromise their vaccination-induced immunity. Although small decreases in vaccine efficacy are usually not a major public health concern, in these patient populations even a small decrease in efficacy could translate into a large increase in morbidity. Patients in long-term care facilities, dialysis units, oncology clinics and transplant programs are examples of such populations.

Innovative Health System (IHS) aims to design a process for safe, effective, cost-Effective and equitable innovation. The promise of products for the human microbiome and products that support mucosal immune function are two areas of novel therapies that could be explored in research and clinical practice. Decisions regarding patient selection, avoiding unnecessary tests and unsafe products, will be key considerations. As the field of microbiome research grows, clinicians will increasingly encounter patients who have purchased stool tests, immune panels and other marketed “microbiome therapies” and will need clear policies that differentiate low-value practice from evidence-based practice.

Who It Affects

Those with low levels of IgA whether selectively low (IgAD) or as a result of some secondary process are affected by IgA Deficiency. Selective IgA deficiency is one of the more common of the primary immune deficiencies and in many cases, individuals with this condition are completely asymptomatic. However, some individuals with selective IgA deficiency can be plagued by recurrent respiratory or gastrointestinal infections, chronic diarrhea, sinusitis or have a poor response to vaccines. A diagnosis of secondary IgA deficiency must also be considered in those individuals with conditions that decrease IgA levels such as certain medications, malignancies, conditions which result in protein-losing enteropathies, severe malnutrition and other diseases which may alter immune function. The diagnosis of IgA deficiency must be considered in the context of the patient’s clinical presentation, which may include symptoms of recurrent infections, inadequate response to vaccines, or chronic mucosal inflammation.

1) Infants and young children

The first years of life are critical for the assembly of the human microbiota and the corresponding development of the immune system. The establishment of microbial communities and mucosal immunity are complex processes that are influenced by a variety of factors, including the infant’s diet, episodes of illness, antibiotic use and environmental exposures. IgA in human milk is one of the key components of mucosal immunity and provides the infant’s mucosal tissues with protection against infection. Understanding the influences on immune development in the early years of life is of growing interest to pediatric clinicians who are now wondering how exposures such as early antibiotics, recurrent gastrointestinal illness and poor growth affect a child’s ability to respond to vaccines.

The mis-understanding that patients and families have about vaccination is not limited to their understanding of its benefits and risks. Both patients and families can mistakenly attribute illness (in severe cases, even death) to vaccines, or believe that they or their children became sick because they did something wrong. By having a clear understanding of the concept of nonresponse to vaccines and some of the underlying reasons for nonresponse, this mis-understanding and its impact on patient and family education can be alleviated.

2) Older adults

Older individuals may experience a double hit to their immune systems. First, immune aging impairs both the initial and subsequent immune responses. Immune memory – the pool of “memory” T cells capable of mounting a swift defense against previously encountered pathogens – also declines with age, while gene expression of inflammatory genes is increased. Older individuals also have decreased diversity in their gut microbial community, or ecosystem. That shift may also decrease vaccine effectiveness. Many older individuals are taking medications such as proton pump inhibitors that decrease stomach acid, antibiotics or anti-inflammatory medications that can decrease the gut microbial ecosystem. These individuals are already considered a high-priority group for vaccination against the flu, pneumococcal disease, shingles, COVID-19 and other pathogens. Understanding how such factors may reduce the effectiveness of vaccine responses is critical to developing optimal preventive strategies for this age group.

3) People with chronic disease or immunosuppression

Patients on immune-modifying therapy for cancer or transplantation may have impaired mucosal hosts and abnormal microbiota. Chemotherapy, biologic agents, corticosteroids, and immunosuppressive medications have well-documented effects on antibody production and immune function. Patients typically receive antibiotics for their infections, and frequently are on less than optimal nutritional diets during their acute illness. The clinician must be more aware of the decreased vaccine responses in patients who are on immune-modifying therapy. Additionally, post-vaccination serology may be indicated. Patients on immune-modifying therapy may require earlier additional preventive measures in the event of an outbreak.

4) Patients who have had multiple illnesses or known vaccine failures.

Infection with a pathogen that the patient has been vaccinated against needs to be assessed as to its significance and potential causes. While a few obvious factors can be mentioned, such as the timing of the vaccination and the strain of the vaccine used, it is generally more complex. Other potential contributing factors include the person’s immune status, level of exposure to the pathogen, and vaccination and illness history. In assessing immune function, it is advisable to consider more than just the levels of the traditional immunoglobulins. Events that lead to illnesses that vaccines prevent need to consider the potential role of decreased balance of the human microbiota. Cases of repeated pneumococcal infections, severe influenza illness in the wake of recent vaccination for the same virus, and multiple cases of pertussis-like illness in someone who has been vaccinated against pertussis are examples of such events.

5) Clinicians, health systems, and payers

Teams focused on primary care, infectious disease, immunology, and geriatrics will be deluged with patients and families seeking information on various immune issues. As people become more informed about the microbiome they will ask staff for information about probiotics, stool tests, diet plans and various supplement schemes related to immune issues. Staff will need to provide consistent patient education regarding immune issues, make evidence-based decisions, and assist with referral to appropriate services. Payers will face tough decisions about coverage for various immune tests, vaccine doses and emerging treatments targeted to the microbiome.

What Changes

Research to identify the determinants of vaccine responsiveness continues. However, as our knowledge expands, screening for particular risk factors before administration of specific vaccines may become part of clinical practice. For the vast majority of children and adults, the conventional vaccines (dTap, MCV4, etc) can be given without assessment of immune function. In the patient(s) who demonstrates vaccine nonresponse and in the patient with a history suggestive of immune deficiency, measurement of immunoglobulin levels, review of prior vaccine responses and the patient’s history of illness may provide some insight. The practicing clinician must also understand that isolated low IgA levels do not mandate therapy but in the proper clinical context can be useful diagnostic tools.

1) A practical approach to suspected vaccine nonresponse

For those patients whose course does not follow the expected pattern of illness or recovery, there are established pathways of evaluation and management. A practical approach to diagnosing illness that is not quite right would involve identifying possible causes based on the patient’s and exposure history, reviewing factors such as whether the patient has been vaccinated appropriately and if enough time has elapsed for immunity to have developed. Additionally, one might check for possible errors in storage (for vaccines that are temperature sensitive) and evaluate for prior immunity to the specific pathogen. Initial trials of management would include measuring total immunoglobulins and specific vaccine titers and performing tests to evaluate for underlying medical conditions that might impair immune function. Based on these results, the provider could decide on a course of action such as administering additional vaccine boosters, trying a different vaccine, or referring the patient to Immunology.

Counsel patients whose slow vaccine titres may be immune-mediated, medication-induced or exacerbated by chronic inflammation. Patients with concerns about vaccination may appreciate accurate information to alleviate vaccination-related anxiety and guide behaviour to adhere with vaccine recommendations.

2) Microbiome-informed prevention strategies may expand

Diet and lifestyle counseling may play an increased role in vaccine planning. While diet won’t replace vaccines, it can help boost immunity, and a high-fiber diet may support a robust variety of microbiota. Sleep, physical activity, and stress also greatly affect immune function and gene expression. The most practical advice clinicians can offer their patients is to get enough sleep and eat a healthy diet/lifestyle. Patients may be seeking probiotics to support their bodies’ response to vaccines, and it’s important that clinicians understand there are some data on this topic, with different outcomes for different strains, and not all products are indicated for use in the immunocompromised patient.

Future immunization recommendations may place more emphasis on proper use of antibiotics (i.e. antibiotic stewardship) and maintaining a healthy balance of normal flora. Parents and patients can expect some side effects when antibiotics are truly indicated, but there are steps all of us can take to feel better sooner. Understanding how diet can contribute to recovery and being aware of potential complications can help patients and families feel empowered. Counsel on these topics represents a low cost yet effective system-level intervention designed to meet a variety of goals.

3) Evidence, regulation, and safety information for adjunctive therapies.

While there is much interest in escalating the intensity of the microbiome-directed therapies already available, their use should be carried out with caution and respect for their limitations. Targeted prebiotics, strain-specific probiotics and microbiota transfer are by and large highly empirical and very complex treatments with the potential for transmission of infection, metabolic complications, or worsening of clinical symptoms in the most vulnerable of patients. It is crucial for the health systems in which we practice to establish governance policies and procedures that limit off-label or unregulated use of these very promising emerging therapies and promote the use of evidence-based treatments whenever possible.

IgA replacement therapy is not simply a matter of finding a replacement product for the clinician. Present day immunoglobulin (Ig) products are primarily designed to replace IgG and provide no mucosal IgA replacement or restoration of mucosal immunity. Future replacement therapies may include administration of IgA as well as other approaches to enhancing mucosal immunity that need to be followed by well-designed clinical trials to assess safety and efficacy. Indications for use and criteria for selection of patients as well as cost-effectiveness need to be developed.

4) Vaccination guidance may become more personalized

Schedules and follow up can be modified for high risk patients. A personalied vaccine strategy could include longer intervals between vaccine doses, or administration of higher dose or adjuvanted vaccines (such as pneumococcal conjugate). Post-vaccination serology can be arranged for individual patients and immunosuppression timing planned accordingly. We aim to make vaccination as simple as possible for all patients, while ensuring optimal protection for those most likely to respond poorly.

Better monitoring of vulnerable subpopulations could improve the effectiveness of public health interventions. Improved surveillance of effectiveness in high-risk populations through better monitoring of breakthrough infections and waning immunity could help inform policy makers and healthcare providers with earlier insight into protection afforded to vulnerable populations, guiding outbreak planning and revisions to estimates of herd immunity in settings with high levels of immune dysfunction.

5) Equity and access need to be built in as you plan, not assumed and then find out that not everyone can participate or use the skills/produce from the program.

As methods of testing and interventions for preventable infections that address the human immune system, develop as vaccine and microbiome-related treatments, it is possible that inequities could worsen if not all patients and families have access to evaluation of the immune system and access to these interventions. Systems and policies must make sure that all patients and families have equitable access to these interventions for preventable infections. This includes ensuring coverage of clinically indicated immune testing, standardizing referral processes, and providing culturally and linguistically competent patient education materials.

Safety Note: This article is for educational purposes only. Please consult with your health physician before incorporating vaccines, immune system function tests, and supplements into your health plan. These topics are particularly important for babies, older adults, and immunocompromised individuals, and can only be appropriately advised by a licensed physician.

References:

https://pmc.ncbi.nlm.nih.gov/articles/PMC12502822/ https://pmc.ncbi.nlm.nih.gov/articles/PMC12656788/