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In this article, we will discuss the types of immunity. We will also explain that vaccines contain antigens that stimulate immune responses to provide long-term immunity. In the end, we will discuss how vaccination programs can help to control the spread of infectious diseases. So, let us get started.
Types of Immunity
There are two primary types of immunity:
- Active immunity
- Passive immunity
Active Immunity
We acquire active immunity when an antigen enters our body and stimulates a particular immune response (production of antibodies). Active immunity can be acquired in one of the following ways:
- Naturally acquired active immunity: It is acquired when the body is exposed to microbes
- Artificially acquired active immunity: It is gained through vaccinations
A person acquires long-term immunity when the body produces memory and plasma cells. The concentration of antibodies in the blood takes one to two weeks to increase during the primary response to a pathogen or vaccination in an active immunity. If the same pathogen attacks the body again, then during the secondary response, the antibody concentration in the blood increases in a much shorter period. Moreover, during the secondary response, the antibody concentration is higher than during the first infection or after vaccination.
Passive Immunity
This type of immunity is acquired without an immune response. The infected person does not produce antibodies in passive immunity. There are no memory cells that produce antibodies in a secondary response because the immune system of the infected person does not get activated. In case of reinfection, the person would require another infusion of antibodies.
An infected person may not have time to actively acquire immunity because of the nature of the disease, for instance, tetanus. In other words, we can say that there is no time for active immunity. Hence, we can acquire passive immunity in one of the following ways:
- Artificial passive immunity: It is acquired when people are injected/transfused with antibodies. For tetanus, antitoxin is suggested. The antibodies were accumulated from people whose immune system was stimulated by the vaccination to produce tetanus antibodies.
- Natural passive immunity: It is either acquired when fetuses receive antibodies across the placenta from their mothers or babies receive first breast milk from the mothers which pass a specific isotype of antibody.
Working of Vaccination
A vaccine refers to a suspension of antigens that are put intentionally into the body to trigger an artificial active immunity. Vaccines are of two types:
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- Live attenuated
- Inactivated
Vaccines are either given orally or through an injection. The vaccines administered through injection are injected into the muscle or vein.
Long-term immunity is achieved through vaccination because they create memory cells. When the immune system encounters the pathogen again, it remembers the antigen and produces antibodies against it.
How effective vaccines are?
Vaccines can be highly effective even with a single vaccination. They give lifetime protection. Vaccines are generally harmless as they do not cause the disease they are protecting against because the pathogen is killed by the primary immune response.
Problems with Vaccination
Although vaccines give lifetime immunity, however, there are certain problems with vaccines which are explained below:
- People who are given vaccines can have a poor response due to malnourishment. Their body may not be able to produce antibodies or they may have a defective immune response.
- There is a chance of transmitting a live pathogen to others in the population. So, it is recommended that a sufficient number of people in the population should be vaccinated at the same time to achieve herd immunity.
- Antigenic variation: The variation caused by the major changes in the antigens of the pathogens. It causes the vaccines to not stimulate an immune response or diseases caused by the eukaryotes having a huge number of antigens on their cell surface membranes. It makes the production of vaccines difficult would cause the immune system to respond rapidly enough.
- Antigenic concealment: It happens due to one of the following reasons:
- When the pathogen lives inside the cell and thus is hidden from the immune system
- When the bodies of pathogens are coated in host protein or they parasite immune cells such as macrophages and T cells
Live Attenuated Vaccines
- Live attenuated vaccines have entire pathogens, for instance, viruses or bacteria, that have been weakened
- Because the pathogens are weak, therefore they multiply slowly, thus allowing the body to identify the antigens and stimulate the primary immune response.
- Live attenuated vaccines tend to produce a stronger and longer immune response.
- They are not recommended to people who have a weak immune system because the pathogen can divide before enough antibodies can be produced.
- Examples of live attenuated vaccines include MMR (Mumps, Measles, and Rubella)
Inactivated Vaccines
- Inactivated vaccines also contain the whole pathogen like live attenuated vaccines, however, that pathogen is dead or killed. Inactivated vaccines may contain small constituents of pathogens.
- Because inactivated vaccines do not contain living pathogens, hence they are unable to cause disease even in those people who have a weak immune system
- The drawback of these vaccines is that they are not able to trigger a stronger or long-lasting immune response like live attenuated vaccines. Often people require repeated does or booster shots.
- Moreover, these vaccines may trigger an allergic or local reaction in few people because the adjuvants may be joined to the subunit of a pathogen to make the immune response stronger and longer
- A popular example of the inactivated vaccine in which the whole pathogen is killed is a polio vaccine
- An example of a toxoid subunit vaccine is Diphtheria
How do Vaccination Control Diseases?
- Except for smallpox, no other pathogen is completed eradicated globally
- The world got rid of smallpox because the live attenuated vaccine was employed against the only strain of the virus. Moreover, a rigorous program of surveillance, contact tracing, and ring vaccination also played their role in eradicating this disease.
- A large number of safe and effective vaccines have already almost eradicated several childhood diseases
- Vaccines against the common childhood diseases like chickenpox, mumps, and whooping cough are administered to children as part of an immunization schedule and they have successfully delivered immunity
- The vaccines have helped to keep several childhood diseases at low levels within a population.
- Certain vaccines have enabled us to achieve herd immunity. Herd immunity is achieved when a large proportion of the population is vaccinated. Due to this, it is difficult for the pathogen to spread within a population. Even those people in a population who are not vaccinated are unlikely to contract a disease because the level is far too low.
- Although a majority of the vaccines are administered to children, however, some vaccines are administered at later stages in life. Examples include tuberculosis and Hepatitis B.
- Tourists or travellers are advised to take specific vaccines if they are travelling to regions where some diseases are endemic. An example of an endemic includes Yellow fever in some parts of Africa.
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