Trevor James
Vaccines are designed to trigger a primary immune response and generate memory cells without causing illness. They contain weakened or dead forms of a pathogen, which stimulate the innate immune system. The innate immune system provides a first line of defence against pathogenic agents but does not have memory. The adaptive immune system, on the other hand, has memory and can provide a more rapid and effective secondary immune response upon re-exposure to the same pathogen. This secondary immune response is the result of memory cells, which are produced during the primary immune response.
| Characteristics | Values |
|---|---|
| Purpose | Vaccines aim to trigger the body's primary immune response and generate memory cells without causing illness. |
| Function | Vaccines train the body to fight harmful invaders by causing an immune response. |
| Composition | Vaccines contain weakened or dead parts of a particular organism (antigen) that triggers an immune response within the body. |
| Protection | Vaccines provide protection against targeted diseases, but not all vaccines work for everyone. |
| Herd Immunity | Vaccines help protect those who cannot be vaccinated by limiting the circulation of pathogens in a community. |
| Effectiveness | No single vaccine provides 100% protection, but they are still the safest and most effective way to protect against preventable diseases. |
| Doses | The number of doses needed to achieve immunity depends on whether the antigen in a vaccine is alive or not. |
| Primary Response | The first encounter with an antigen, which activates lymphocytes and generates memory cells. |
| Secondary Response | A faster and more effective immune response due to the activation of memory cells created during the primary response. |
| Innate Immune System | The body's first line of defense against pathogenic agents, but it does not have memory. |
| Adaptive Immune System | Interacts with the innate system to provide an effective immune response, producing effector cells and memory cells. |
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What You'll Learn
Vaccines contain weakened or dead pathogens
Vaccines are designed to keep us safe from deadly illnesses without exposing us to the dangers of a full-blown infection. They contain weakened or inactive parts of a particular organism (antigen) that triggers an immune response within the body. Other vaccines contain weakened or reconstituted viruses or bacteria in their entirety.
Weakened vaccines, also known as attenuated vaccines, contain weakened derivatives of a disease-causing pathogen. A pathogen is a foreign body such as a virus or bacteria that elicits an immune response when introduced into the body. The pathogen is carefully weakened in a laboratory-controlled environment, making it strong enough to elicit an immune response, but weak enough to leave the vaccinated person unharmed. The immune system recognises the pathogen as a foreign intruder and produces antibodies against it. After vaccination with a weakened vaccine, the virus or bacteria grows and replicates inside the body. This type of vaccine causes a stronger immune response than dead vaccines and usually provides lifetime protection against a disease with a single dose. However, they require more involved handling and refrigeration to remain weakened and prevent mutation.
Dead vaccines, also called inactivated vaccines, contain dead or inactive forms of a pathogen. These vaccines are made up of pathogens that are completely killed in a lab before administration. The pathogens are destroyed and cannot divide, but they maintain some integrity so that the immune system can recognise and evoke a response. Inactivated vaccines tend to produce a weaker immune response, requiring multiple doses and boosters to provide longer-lasting protection. They are more stable than live pathogens, facilitating easier storage and transport.
Both types of vaccines induce long-term stimulation of the adaptive immune system, leading to the production of effector cells and memory cells. Memory cells are created with the primary immune response, allowing for a faster and more effective secondary immune response during subsequent exposures to the antigen.
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The immune system's primary and secondary responses
The immune system is divided into two main subsystems: the innate (or general resistance) system and the adaptive system. The innate immune system provides a first line of defence against pathogenic agents, but its responses are not specific to a particular pathogen. On the other hand, the adaptive system responds specifically to each pathogen.
The primary immune response is the activation of lymphocytes following the first recognition of foreign material. This initial response generates memory cells, which remain present and available for action long after the initial response activities wane.
Vaccines trigger the primary immune response and generate memory cells without causing illness. They use weakened or dead pathogens, or parts of the virus or bacteria, to mimic the initial exposure to a disease-causing organism. This prompts the immune system to respond as it would have on its first reaction to the actual pathogen. The vaccine enables the production of memory cells, which are specific to the virus or bacteria they identify and destroy.
The secondary immune response occurs when memory cells are reactivated upon encountering the same antigen again. This response is faster, more focused, and more effective than the primary response. Memory cells rapidly proliferate and differentiate into plasma cells, which produce antibodies to clear the antigen.
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Immunological memory
Vaccines are designed to trigger a primary immune response and generate immunological memory without causing the disease. They contain weakened or dead forms of the pathogen and are designed to mimic the initial exposure. This initial exposure stimulates the innate immune system, which then leads to the differentiation of naive T cells and the expansion of T and B cell populations.
The secondary immune response is faster, more focused, and more effective than the original encounter. It is primarily composed of IgG, while the primary encounter elicits IgM-associated responses, followed by a modest IgG response. The secondary response is also characterized by a stronger and more rapid elicitation of IgG, representing immunological memory.
The number of doses needed to achieve immunity depends on whether the antigen in a vaccine is alive or not. Live-attenuated vaccines can provide enduring protection with only two doses, while non-live vaccines typically require at least three doses to achieve protection that fades over time and must be restored with booster doses.
Vaccines are especially useful when there is a limited time window for fighting pathogens, as they can induce protection by raising sustained titers of specific antibody responses in a shorter time frame.
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Live-attenuated vaccines
Vaccines work by imitating an infection, triggering the body's natural defences. The active ingredient in all vaccines is an antigen, which causes the immune system to produce antibodies. Live vaccines use a weakened, or attenuated, form of the disease-causing organism. These vaccines are created by taking a ''wild'' virus or bacteria and attenuating it in a laboratory, usually by repeated culturing. The measles vaccine, for example, was isolated from a child with measles in 1954.
However, live-attenuated vaccines are not suitable for everyone. They can cause a life-threatening infection in someone with a weak or suppressed immune system. People with weakened immune systems, long-term health problems, or who have had an organ transplant, should consult their healthcare provider before receiving a live vaccine. Live vaccines are also fragile and can be damaged or destroyed by heat and light. They must be stored and handled carefully, and kept cool, which means they cannot be used in countries without widespread access to refrigerators.
Examples of live-attenuated vaccines include the MMR (measles, mumps, and rubella) vaccine, the chickenpox vaccine, the varicella vaccine, the rotavirus vaccine, and the influenza (intranasal) vaccine.
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The role of antibodies
The immune system is comprised of two subsystems: the innate (or general resistance) immune system and the adaptive immune system. The innate immune system is the body's first line of defence against pathogens and foreign substances. It acts quickly and non-specifically, ensuring that bacteria are detected and destroyed.
The adaptive immune system, on the other hand, is more specialised. It includes the humoral and cell-mediated arms of the system. The cell-mediated arm, or T-cells, mature in the thymus and are released into the bloodstream. T-cells can be further classified into CD4 cells and CD8 cells. CD4 cells, or T-helper cells, are essential for antibody-mediated immunity and help B-cells control extracellular pathogens.
B-cells, or B-lymphocytes, are created in the bone marrow and mature into specialised immune system cells. They are activated by T-helper cells, which send signals to B-cells that match the same germs. This stimulation prompts B-cells to replicate and turn into plasma cells. Plasma cells then produce antibodies, which are released into the bloodstream.
Antibodies are proteins produced by B-cells that travel throughout the body via the bloodstream. They are the immune system's "soldiers", recognising and neutralising foreign substances. Each antibody is trained to recognise a specific antigen. When the body is exposed to an antigen for the first time, it takes time for the immune system to respond and produce antibodies specific to that antigen. Once the antigen-specific antibodies are produced, they work with the rest of the immune system to destroy the pathogen and stop the disease.
During the primary immune response, naïve B-cells are activated by T-cells. The B-cells then proliferate and undergo somatic hypermutation, changing the affinity of their receptors. B-cells that can bind to antigens subsequently receive survival signals from T-cells, while those that cannot bind or bind weakly undergo apoptosis. B-cells will also class switch from IgM to other antibody types, such as IgA or IgG. After these processes, B-cells differentiate into plasma cells and memory B-cells.
The memory B-cells produced during the primary immune response enable a more rapid and effective secondary immune response. When these memory B-cells encounter their specific antigen again, they quickly proliferate and differentiate into plasma cells, which produce antibodies to clear the antigen. Memory B-cells can survive for decades and respond to multiple exposures. With each subsequent exposure, the affinity and amount of antibodies increase, leading to a faster and more robust immune response.
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Frequently asked questions
Primary immune response refers to the activation of lymphocytes when the body encounters foreign material for the first time. This first encounter with an antigen elicits IgM-associated responses, followed by a modest IgG response. Memory cells are then generated, which remain in the body long after the initial response activities wane.
A secondary immune response occurs when the body encounters the same antigen for a second time. This secondary response is faster, more focused, and more effective than the original encounter. Memory cells are engaged and activated, and the reaction is primarily composed of IgG.
Vaccines contain weakened or inactive parts of a pathogen (antigen) that triggers an immune response within the body. Vaccines can also contain a weakened or reconstituted virus or bacteria as a whole. The body responds to the vaccine as if it were fighting a mild form of the germ. This immune response causes mild symptoms in some people, such as fever, chills, or tiredness.
Vaccines aim to trigger a primary immune response and generate memory cells. When the body encounters the antigen in the vaccine, B-cells and T-cells are activated and produce antibodies to fight off the infection. The body then adds memory cells to its toolbox, which keep a lookout for the pathogen. If the body encounters the same pathogen in the future, a secondary immune response is activated, which is quicker and more effective than the primary response.
