Active Immunization, Working, Examples, Advantages and Drawbacks

Active immunization, also known as immunization or vaccination, is a medical intervention aimed at stimulating an individual’s immune system to develop an active immune response against a specific pathogen, such as a virus or bacteria. This process provides protection against future infections with the same pathogen.

Active immunization involves the administration of a vaccine, which contains either weakened or inactivated forms of the target pathogen, specific components of the pathogen, or genetically engineered antigens that mimic the pathogen. These components are chosen to elicit an immune response without causing the actual disease.

Working of active immunization:

1. Introduction of Antigen: The vaccine is administered through injection, oral ingestion, or nasal spray. The vaccine contains antigens that are recognized by the immune system as foreign substances.
2. Immune Response Activation:
   • The immune system recognizes the antigens as potential threats and initiates an immune response.
   • B cells are activated to produce antibodies specific to the antigen.
   • T cells are activated to support the antibody response and facilitate cellular immunity.
3. Antibody Production:
   • B cells differentiate into plasma cells, which are specialized cells that produce and secrete antibodies. These antibodies are specific to the antigens in the vaccine.
4. Immunological Memory:
   • Memory B cells and memory T cells are generated during the immune response. These cells “remember” the specific antigens and provide long-lasting immunity.
5. Protection Against Future Infections:
   • If the vaccinated individual is later exposed to the actual pathogen, the immune system can mount a rapid and robust response, preventing or mitigating the development of the disease.

Active Immunization Examples:

1. Measles, Mumps, and Rubella (MMR) Vaccine:
   • Protects against measles, mumps, and rubella (German measles).
2. Polio Vaccine:
   • Protects against polio (poliomyelitis).
3. Hepatitis B Vaccine:
   • Protects against hepatitis B, a viral infection that affects the liver.
4. Diphtheria, Tetanus, and Pertussis (DTaP) Vaccine:
   • Protects against diphtheria, tetanus (lockjaw), and pertussis (whooping cough).
5. Haemophilus influenzae type b (Hib) Vaccine:
   • Protects against Haemophilus influenzae type b, which can cause severe infections like meningitis.
6. Pneumococcal Conjugate Vaccine (PCV):
   • Protects against infections caused by Streptococcus pneumoniae bacteria, including pneumonia and meningitis.
7. Rotavirus Vaccine:
   • Protects against rotavirus, a leading cause of severe diarrhea in infants and young children.
8. Influenza Vaccine:
   • Protects against seasonal influenza viruses. The vaccine is updated annually to match circulating strains.
9. Human Papillomavirus (HPV) Vaccine:
   • Protects against certain types of HPV that can lead to cervical and other cancers.
10. Meningococcal Vaccines:
    • Protect against Neisseria meningitidis bacteria, which can cause meningitis and septicemia.
11. Varicella (Chickenpox) Vaccine:
    • Protects against the varicella-zoster virus, which causes chickenpox.
12. Hepatitis A Vaccine:
    • Protects against hepatitis A, a viral infection that affects the liver.
13. COVID-19 Vaccines:
    • Protect against the SARS-CoV-2 virus, which causes COVID-19. Various vaccines, such as those developed by Pfizer-BioNTech, Moderna, and others, have been authorized for emergency use.
14. Tuberculosis (BCG) Vaccine:
    • Provides partial protection against tuberculosis, caused by the bacterium Mycobacterium tuberculosis.
15. Yellow Fever Vaccine:
    • Protects against yellow fever, a viral hemorrhagic fever transmitted by mosquitoes.

Advantages of Active Immunization:

1. Disease Prevention and Control:
   • Vaccination helps prevent and control the spread of infectious diseases, reducing the incidence and severity of illnesses.
2. Eradication of Diseases:
   • Vaccination programs have led to the eradication of certain diseases, such as smallpox, and have brought the world close to eradicating polio.
3. Protection of Vulnerable Populations:
   • Vaccination provides protection to individuals who may be more susceptible to severe complications from certain diseases, such as infants, elderly individuals, and those with weakened immune systems.
4. Herd Immunity:
   • Vaccination contributes to herd immunity, where a sufficient proportion of the population is immune to a disease, making it harder for the disease to spread. This helps protect individuals who may not be able to receive vaccines.
5. Cost–Effective:
   • Vaccination is generally more cost-effective than treating and managing diseases after they occur. It saves on healthcare costs associated with treating severe cases and long-term complications.
6. Convenience and Accessibility:
   • Vaccines are often readily available and can be administered in various healthcare settings, making them easily accessible to a wide population.
7. Reduced Social and Economic Impact:
   • By preventing illness and reducing the burden of diseases, vaccination helps maintain a productive and healthy workforce, contributing to economic stability.

Disadvantages of Active Immunization:

1. Possible Side Effects:
   • Some individuals may experience mild side effects after vaccination, such as pain or swelling at the injection site, mild fever, or fatigue. Serious side effects are rare.
2. Allergic Reactions:
   • Although extremely rare, some individuals may have severe allergic reactions to components in vaccines. These reactions are usually identified and managed in healthcare settings.
3. Vaccine Failures:
   • While vaccines are highly effective, no vaccine is 100% foolproof. In rare cases, vaccinated individuals may still contract the disease, but the severity is often reduced.
4. Need for Multiple Doses:
   • Some vaccines require multiple doses to provide full protection. This can be a logistical challenge, especially for certain populations or in regions with limited healthcare resources.
5. Fear and Vaccine Hesitancy:
   • Misinformation, fear, or mistrust of vaccines can lead to vaccine hesitancy, which can result in lower vaccination rates and reduced herd immunity.
6. Cold Chain Requirements:
   • Some vaccines, especially those using live, attenuated viruses, require specific storage and transportation conditions, known as the cold chain. Maintaining these conditions can be a logistical challenge in some regions.

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