Precautions for Vaccinating Immunocompromised Individuals

Vaccination serves critical purposes in public health, including disease prevention, immunotherapy for conditions like cancer, and efforts to eradicate diseases such as smallpox. It also controls disease transmission by achieving high vaccination rates and protecting vulnerable individuals who cannot be vaccinated. These efforts contribute significantly to global health by reducing illness, saving lives, and fostering healthier communities. 

Immunosuppressed individuals face unique challenges regarding vaccination compared to immunocompetent individuals. Due to their compromised immune systems, they may not respond as effectively to vaccines and are at higher risk for vaccine-preventable diseases.

Individuals with immunological challenges can generally be categorized into two main groups: the immunosuppressed and the immunocompromised. Immunosuppressed individuals have intentionally suppressed immune systems, often due to medications like corticosteroids or chemotherapy, or following organ transplantation. On the other hand, immunocompromised individuals have weakened immune systems due to conditions such as HIV/AIDS, genetic disorders affecting immune function, or certain cancers.

The decision to vaccinate immunosuppressed individuals requires careful consideration of their specific medical condition, the type of vaccine, potential risks, and benefits. Consulting with a healthcare provider specializing in immunocompromised conditions is crucial to determine the appropriateness and timing of vaccinations for these individuals.

A vaccine is a biological substance(antigen) that stimulates the immune system by introducing a weakened or inactive pathogen to the body, training the immune system to recognize and fight the disease in the future. They are basically divided into two types: inactivated and live attenuated. Inactivated vaccines are made from microorganisms (viruses, bacteria, etc.) that have been killed by physical or chemical methods, rendering them unable to cause disease.

Immunocompromised as well as immunocompetent individuals residing with immunocompromised patients can safely receive inactivated vaccines. Inactivated vaccines do not contain live pathogens and thus do not pose a threat of causing illness in immunocompromised individuals. This precaution ensures that they minimize the risk of transmitting vaccine-preventable diseases to vulnerable individuals. 

Live attenuated vaccines are made from disease-causing viruses (Wild type) or bacteria that have been weakened in a controlled environment. Live attenuated vaccines replicate in the host but do not cause severe disease like the wild-type organism. They stimulate immunity similarly to natural infections and, therefore, can cause mild symptoms similar to the natural disease. This poses a risk for immunocompromised individuals whose weakened immune systems may struggle to control even weakened pathogens. In such Individuals, even the attenuated antigens ( bacteria or viruses) can replicate and produce symptoms due to their weak immune conditions. 

For instance, in cases of persistent infections such as tuberculosis, administration of the BCG vaccine can result in complications such as localized lymphadenitis or even disseminated infections. Another issue involves the potential contamination of vaccines produced in tissue cultures; if these cultures are contaminated, vaccines may harbour other viruses such as retroviruses, as observed in historical instances involving the measles vaccine.

Similarly, due to safety considerations, live attenuated vaccines (LAVs) are typically avoided during pregnancy to prevent any potential risks to the developing fetus. These precautions are crucial in ensuring vaccines are safe and effective for all individuals, especially those with compromised immune systems or during sensitive periods like pregnancy.

Vaccination recommendations for immunocompromised individuals depend on their specific health conditions and medical guidance. Adjustments to vaccination schedules may be necessary to ensure optimal protection without compromising health. Generally, live vaccines should be administered at least four weeks before starting immunosuppressive therapy and avoided within two weeks before initiation. Inactivated vaccines should ideally be given at least two weeks before immunosuppression. Additionally, immunocompetent individuals who reside with immunocompromised persons should seek advice from healthcare professionals before receiving vaccinations. 

Therefore, individuals with compromised immune systems should be mindful of these guidelines before undergoing any vaccinations.

Immune Amnesia Associated with Measles

 The immune responses triggered by measles virus (MV) infection can unexpectedly suppress the body's ability to respond to other unrelated antigens, a condition that may persist for weeks to years after the acute illness subsides. This immune suppression significantly increases vulnerability to secondary bacterial and viral infections such as pneumonia and diarrhea, which are major causes of illness and death following measles.

Measles infection disrupts delayed-type hypersensitivity (DTH) responses to known antigens like tuberculin, and impairs both cellular and humoral responses to new antigens. This immune dysregulation also contributes to the reactivation of tuberculosis and the worsening of autoimmune diseases post-measles.

In essence, measles-induced immune suppression not only weakens immediate defenses against pathogens but also compromises the immune system's ability to mount effective responses to a range of antigens over an extended period.

Measles-induced immune suppression can occur due to changes in antigen-presenting cells or effector lymphocytes, or through the depletion of CD150+ memory lymphocytes. Measles virus (MV) infects CD150+ immune cells, including memory T- and B-lymphocytes. Studies comparing blood samples collected from unvaccinated children before and after measles reveal incomplete reformation of B-lymphocyte pools post-infection. Additionally, measles leads to a significant reduction in circulating antibodies against various viruses and bacteria, impairing immunological memory and causing what is termed 'immune amnesia'.

This mechanism contributes to increased childhood morbidity and mortality for more than two years after measles infection. Abnormalities in both innate and adaptive immune responses are evident following MV infection. Children commonly experience transient lymphopenia, characterized by decreased T and B lymphocytes in the blood. Furthermore, immune cells such as dendritic cells, crucial for presenting antigens to lymphocytes, show impaired maturation and reduced ability to stimulate lymphocyte proliferation.

In summary, measles disrupts immune function by compromising both cellular and antibody-mediated immunity, leading to prolonged susceptibility to infections and contributing to the severity of measles-related complications in children.

Subacute sclerosing pan encephalitis (SSPE): Persistent measles Virus infection

Subacute sclerosing pan encephalitis (SSPE), also called Dawson’s encephalitis, is a persistent measles infection of the central nervous system. SSPE is a progressive, fatal, encephalopathy characterized by personality changes, mental deterioration, involuntary movements, muscular rigidity, and death. SSPE usually begins 4–10 years after the patient has recovered from naturally acquired measles.
Successful isolation of measles virus from brain and lymphoid tissues of SSPE patients clearly established measles virus as the etiologic agent of the disease. Molecular characterization of measles virus nucleic acid sequences derived from brain biopsy or autopsy has identified wild-type measles sequences with few exceptions, and not those of the vaccine strains.
Measles virus genotypes found in association with SSPE clinical specimens are generally the circulating sequences, in the geographic region where the patients acquired natural infection. No vaccine sequences were identified from tissues of SSPE patients.
SSPE is a very rare but lethal disease, persisting in the human central nervous system (CNS). It is characterized by the absence of viral budding, reduced expression of the viral envelope proteins and spread through the CNS despite massive immune responses. The persistence of measles virus in the brain cells may be due to mutations in the MV genes that were introduced not only due to errors of the MV polymerase, but also in clusters due to hypermutations. The other reasons may be the MV matrix (M) gene, which is most heavily mutated, mutation in the transmembrane glycoproteins, which may be the cause of genetic defects in the persisting measles virus.
The diagnosis is clinical and immunological evidence of measles infection. Management of the disease includes seizure control and avoidance of secondary complications associated with the progressive disability.
Treatment with interferon, ribavirin, and Isoprinosine have reported to give beneficial results. However, the disease shows continuous progression; only 5% of individuals with SSPE undergo spontaneous progress, with the remaining 95% dying within 5 years of diagnosis.