What is Immunisation?

Immunization, or vaccination, protects individuals against infectious diseases by exposing them to a weakened form or a part of a bacteria or virus. Immunization can be through actual infection or vaccines, whereas vaccination involves using the vaccine, though both terms are used interchangeably. Vaccination started with the smallpox vaccine introduced in the late 1700s by Edward Jenner, saving millions from illness and death. With the advancement of science, there is now a vaccine to protect against infectious diseases.

How does a vaccine work?

Through vaccination, small quantities of easily identifiable proteins specific to a pathogen are introduced into the body. These proteins and sometimes cell wall components are made up of complex sugars and interact with the cells of the immune system. When the antigen interacts with the immune cells, the immune cells secrete a substance against these foreign agents called antibodies. 

Antibodies are also proteins that identify and target the pathogen causing the disease. They mark the cells to be destroyed by the immune cells. Once exposed to a particular pathogen, the body develops a memory of the particular antigen.

The next time the same virus or bacteria attacks the body, the immune system responds more intensely. Normally, it would take an infection by a pathogen to initiate antibody formation in the body against it. 

However, with vaccines, the body artificially develops an immune response to the pathogen by recognizing the antigen injected by the vaccine. This is how a person can become resistant to a virus or bacterial infection without exposure.

Immunization vs Vaccination

Vaccination is the process of inducing immunity against an organism or pathogen by injecting small doses of artificially prepared vaccines at specific times. This helps in developing antibodies against the particular pathogen without actually getting infected. Immunization is the process of developing an adequate immune response to pathogens through exposure to natural infections or vaccines.

What are the types of immunizations?

Immunization can be of two types based on how the immunity is acquired:

• Active immunization: wherein the body develops immunity to a particular pathogen after being infected.
• Passive Immunization: wherein the body develops immunity to a particular pathogen by administering the vaccine.

What are the routes through which vaccines can be administered?

Vaccines can be administered through the following routes:

1. Nasal vaccines like smallpox and influenza.
2. Intradermal injection, as in the case of Japanese encephalitis, hepatitis A, and hepatitis B.
3. Drops, as in the case of polio and rotavirus.
4. Intramuscular injection, as in the case of tetanus and the COVID-19 vaccine.

Benefits of Immunization:

The benefits of immunization encompass the spheres of individual and community health. It's a very economical health measure, reducing morbidity and mortality worldwide.

1. Preventing infections: Vaccines are the biggest role in preventing various deadly infections like rabies and tetanus with a simple shot in the arm.
2. Reducing hospitalization: taking flu vaccines before flu season and pneumococcal vaccine shots in smokers and people with lung disease can help prevent hospitalization, saving money and resources.
3. In the case of some vaccines, like polio vaccines, vaccination of an individual or a few individuals can spread immunity to an entire community, thus keeping everyone safe, especially in pandemic-like situations.
4. Lighter on the pocket: Vaccination is a health measure that safeguards against several prevalent and potentially fatal diseases. A simple vaccine can help reduce money spent on diagnosing, treating, and rehabilitating the same disease.
5. Preventing Health Emergencies: Infections tend to spread in the community. A single case of polio or H1N1 can infect hundreds of others, burdening people and the healthcare system. However, it would not be so if the same community was vaccinated.
6. Eradication of Disease: Vaccination has helped eradicate many severe life-threatening diseases like smallpox, polio, and even Japanese encephalitis. This happened because of regular mass vaccinations for generations. Even the COVID-19 pandemic could be controlled by the use of vaccines, saving millions of people and making it a seasonal flu rather than a global health emergency. It is because of the above reasons that the World Health Organisation and the Centres for Disease Control spent millions of dollars on the research and development of vaccines.

What are the diseases that can be prevented by vaccination?

The following are some of the diseases that vaccines can easily prevent:

1. Measles
2. Polio
3. Hepatitis B
4. Pneumococcal pneumonia
5. Tetanus
6. Yellow fever
7. Japanese encephalitis
8. Pertussis 
9. Milliary tuberculosis
10. Influenza
11. H1N1
12. Chickenpox
13. Rotavirus
14. Meningitis

All these diseases can cause severe illness with residual handicaps as well. However, timely vaccination can prevent all of these infections.

Side effects of Vaccination:

The side effects from vaccines can be categorized into common and rare side effects, which are as follows:

1. Nausea
2. Headache
3. Mild Fever
4. Pain at the site of the injection
5. Redness at the site of injection
6. fatigue 

All of these are common side effects seen in the administration of vaccines. Everyone may have a different reaction to the same vaccine, and you can discuss the side effects with your healthcare providers. Rarely, seizures, paralysis, high fever, and anaphylaxis may happen in some individuals, especially those with a background of allergic reactions, neurological disease, or an immune-compromised state.

Is there any population that should avoid vaccination?

Vaccines are generally safe for the majority of people. However, for some people, it can cause very serious consequences.

1. Immunocompromised individuals: These people have a poor immune system, and administration of vaccines, especially live vaccines, can, in fact, cause an infection in them rather than prevent it.
2. In people with severe allergic reactions to the previous dose, the subsequent dose of the vaccine is contraindicated.
3. Some vaccinations are contraindicated in pregnancy as they may pose a risk to the developing fetus.
4. Some vaccines should be avoided in people with cerebral palsy, seizures, and a history of Gillian-Barre syndrome.