Age-Related Immune Changes and Vaccine Efficacy

Introduction:

Aging is a natural inevitable progressive process that causes the decline of biological functions and other abilities. The immune system which protects the human body from various infections may also get worsened when a person approaches old age. The immune system has its maximum function during adolescence and gradually declines when age advances. Age-related immune dysfunction is also known as immune senescence and is characterized by low resistance to infections and the development of autoimmune disorders. As the functioning of the immune system gets affected, the effect of vaccination also decreases in older adults.

How Aging Affects the Functioning of the Immune System?

• Hematopoietic stem cells (HSCs) produce both myeloid and lymphoid lineage cells. Granulocytes, red blood cells (RBCs), monocytes, and dendritic cells belong to the myeloid lineage whereas lymphocytes (B and T) and natural killer (NK) cells belong to the lymphoid lineage. In young adults, the production of both myeloid and lymphoid lineage cells is high with predominant production in lymphoid lineage. B and T lymphocytes, natural killer cells, monocytes, and neutrophils contribute to immune response. In young adults, the production of lymphoid lineage cells is high compared to the production of myeloid lineage cells. In contrast, in older adults, the production of myeloid cells is high and there is a huge decline in lymphoid lineage cells which in turn reduces their immunity. Also, studies revealed that the myeloid cells produced excessively in older adults were not found to be efficient.

• B and T cells play an essential role in immunity. They are made in the bone marrow and thymus and relocated to the spleen. This process is very efficient in young adults. But in older adults, it is less efficient due to the involution of the thymus.

• Another cause under discussion is the impairment of endocrine function during old age. Growth hormone and insulin-like growth factor 1 (IGF-1) help in thymopoiesis (production of T- cells). As their production declines during old age, the production of T-cells also gets affected.

• Inflammaging is a newly discovered phenomenon where the level of pro-inflammatory markers rises as age advances. It can increase the risk of age-related chronic disorders. Inflammaging is now considered an important characteristic of aging in humans.

• Complementary proteins secreted by the liver help in fighting infections and maintaining homeostasis. In older adults, complementary proteins are reduced.

What Are the Consequences of a Weakened Immune System in Older Adults?

Due to weakened immune systems, older adults are more likely to develop infections and other chronic disorders.

• When the ability of the immune system to differentiate between self and non-self cells reduces, the probability of developing autoimmune disorders increases in old age. Giant cell arteritis, Sjogren’s syndrome, rheumatoid arthritis, psoriasis, etc. are common autoimmune disorders in older adults.

• Apart from the difficulty in differentiating self and non-self cells, the weakened immune system also faces trouble in detecting cell defects and correcting them. This can increase the chances of cancer in older adults.

• Older adults with low immunity are susceptible to pneumonia, urinary tract infections, gastrointestinal infections, influenza, etc

• A weak immune system can interfere with the healing process. All the phases of the wound healing process get slowed or impaired during old age. Besides, a weak immune system, it is also attributed to thin skin, delayed inflammatory response, and different collagen.

• Blood disorders like thrombocytopenia (low platelet count) and anemia can occur.

How Does the Weakened Immune System Impact Vaccine Efficacy?

When vaccines are found to be highly effective in children, adolescents, and adults, it is not highly effective in older people. The main reason for low vaccine efficacy in older adults is inflammation. The antibodies produced in response to vaccination in the body of older adults are less effective. Immunosenescence or decreased immunity as age advances is also associated with increased infections, inflammatory diseases as well as low efficacy of vaccines. It affects both innate and acquired immunity in older people. The decrease in adaptive immunity reduces the responses and longevity of vaccines in them.

However, the following measures are taken by healthcare professionals to improve vaccine efficacy in older adults;

• Booster Dose: Primary immunization may be less effective in many individuals. To enhance the effectiveness of the vaccine providing a second dose after one month is found to be useful.

• Time of Vaccine Administration: Studies have shown that the influenza vaccine administered during the morning had more efficacy than the one administered during the afternoon.

• Stress: Individuals with more stress or mental illnesses were found to be less responsive to vaccines. So reducing stress may improve vaccine efficacy.

• Adjuvants: The addition of flagellin, a structural protein are effective in boosting the efficiency of vaccines.

• Exercise: Exercising and good physical activity can improve immunity as well as vaccine efficacy in older adults.

How to Overcome Age-Related Changes in Immunity?

• Get vaccinated regularly. It is important not to miss vaccination schedules even if it is not found to be useful. However, it can lower the severity of many diseases like pneumonia, flu, shingles, etc.

• Eat a healthy and balanced diet. Consuming foods like yogurt, green tea, broccoli, almonds, banana, ginger, almonds, citrus fruits, etc. can improve immunity.

• Avoid smoking as it can weaken the immune system.

• Limit or avoid the intake of alcohol. Like smoking, alcohol can also interfere with immune functions.

• Exercise regularly and be physically active. Exercise can cause changes in white blood cells which in turn can boost immunity.

• Stay away from people with infections and wash one's hands properly to avoid getting infected.

• Get enough sleep. During sleep, proteins called cytokines are produced which prevents infection and inflammation. Studies showed that sleep deprivation can result in low immunity.

• It is mandatory for adults with diabetes or heart conditions to get vaccinated for various infections because they are more prone to infections and other complications in their old age.

• It is important to remain up-to-date with the recommended vaccines.

• Another approach to improve immunity in older people is caloric restriction. Studies revealed that caloric restriction has improved the production of T-cells. However, it also reduced the IGF-1 factor which made the studies more puzzling.

Conclusion:

Impairment of immune functions is one of the most severe consequences of aging in human beings. Hence, older people are more susceptible to infections, inflammations, and chronic diseases. A weak immune system can also result in low responses toward vaccines. As a result, the efficacy of vaccines is less in older adults than in young adults. However, with strategies like booster dose, time of administration of the vaccine, and adjuvants the efficacy of vaccines can be enhanced. To improve immunity and lifestyle during old age, healthcare professionals recommend following a healthy lifestyle and proper vaccination schedules.