Immunization

Introduction

Immunization, also known as vaccination, is a cornerstone of public health that prevents and controls the spread of infectious diseases by stimulating the immune system to produce protective antibodies. Immunization programs have led to the eradication of certain diseases and a significant reduction in morbidity and mortality worldwide. Understanding immunization is crucial for medical professionals, especially those in pediatrics, infectious diseases, and public health. This article provides a comprehensive overview of immunization, including its types, function, related studies, treatment considerations, and clinical significance.

Active vs Passive Immunity

Immunity can be either active or passive with several notable differences

Differences Between Active and Passive Immunity
Feature	Passive	Active
Acquisition method	Receiving preformed antibodies	Exposure to infection or to foreign antigens
Examples	Maternal IgG crossing placentaBabies getting IgA in breast milkAdministration of antitoxin	Infection with the specific pathogenAdministration of a vaccine
Onset	Immediate upon administration	Slow to allow for development of full immune response
Duration	Very short with a half life between two weeks and four weeks	Long or even lifetimeDue to generation of memory

Viral Vaccines

• Viral vaccines can either be live attenuated or killed with several notable differences

Differences between Live and Killed Vaccines
Feature	Live	Killed
Production method	Design a nonpathogenic version of a virus that can still grow transiently in the host	Inactive pathogen or pathogen antigens by treatment with heat or chemicals
Pros	Induce both cellular and humoral responsesinduces lifelong immunity (usually)	Safer than live vaccines because they cannot revert to pathogenic state
Cons	Cannot give to immunocompromised patientsSmall chance of reverting to pathogenic state	Weaker response (usually only humoral)May require booster shots
Examples	Everything elseMMRVZVPolio (Sabin)Etc	Rest In Peace Always RabiesInfluenzaPolio (Salk)Hepatitis A

Bacterial Vaccination

• Bacterial vaccination involves administration of characteristic protein which can be
  • inactivated toxin produced by pathogen called a toxoid
  • coat protein that surrounds the pathogen called a capsule
  • other important proteins that are conserved by the pathogen
• Select examples of vaccines against pathogenic bacteria include
  • DTaP that is composed of
    • C. diptheriae toxoid
    • C. tetani toxoid
    • B. pertussis toxoid
  • H. influenzae capsular type B
  • S. pneumoniae that comes in two forms including
    • a pediatric version with
      • 7 capsule types
      • think: a 7 year old gets PCV
    • an adult version with
      • 23 capsular types
  • N. meningitidis with 4 capsular proteins
• Parenterally delivered vaccines are not effective against mucosal bacteria due to inferior secretory IgA response 
  • Examples of mucosal bacteria
    • E. coli
    • V. cholerae
• Orally delivered vaccines are allow direct antigen contact with mucosa, generating a strong secretory IgA response 

Types of Immunization:

1. Active Immunization: In active immunization, a person’s immune system is exposed to a weakened, killed, or component of a pathogen to trigger an immune response and generate immunity. This immunity provides protection against future infections.
2. Passive Immunization: Passive immunization involves the direct administration of pre-formed antibodies (immunoglobulins) to provide immediate protection against specific diseases. It is used in situations where rapid protection is needed, such as post-exposure prophylaxis.

Function of Immunization:

Immunization serves several critical functions:

1. Preventing Disease: Immunization stimulates the immune system to recognize and remember specific pathogens, preventing future infections.
2. Herd Immunity: Immunization programs create a threshold of immune individuals in a population, reducing the likelihood of disease transmission and protecting those who cannot be vaccinated.

Vaccine Development and Studies:

1. Antigen Selection: Researchers identify key antigens from pathogens that can elicit strong immune responses.
2. Clinical Trials: Vaccine candidates undergo rigorous testing in clinical trials to evaluate safety and efficacy.
3. Long-Term Studies: Post-marketing surveillance monitors the long-term safety and effectiveness of vaccines.

Types of Vaccines:

1. Live Attenuated Vaccines: These vaccines use weakened forms of the pathogen to stimulate a robust immune response. Examples include measles, mumps, rubella (MMR), and oral polio vaccines.
2. Inactivated Vaccines: These vaccines use killed or inactivated pathogens to induce an immune response. Examples include hepatitis A, influenza, and polio (injected) vaccines.
3. Subunit, Recombinant, and Conjugate Vaccines: These vaccines use specific components of the pathogen, such as proteins, sugars, or antigens, to stimulate immunity. Examples include hepatitis B, HPV, and Haemophilus influenzae type b (Hib) vaccines.

Clinical Significance:

1. Disease Eradication: Immunization has led to the eradication of diseases like smallpox and the near-eradication of polio.
2. Reduced Morbidity and Mortality: Immunization programs have significantly reduced the incidence of vaccine-preventable diseases and their associated complications.

Treatment Considerations:

1. Vaccination Schedules: Immunization schedules vary based on age, risk factors, and vaccine availability. They ensure optimal protection over a person’s lifetime.
2. Booster Vaccines: Some vaccines require booster doses to maintain immunity levels.

Future Directions:

1. Improved Vaccine Delivery: Research focuses on developing innovative methods of vaccine administration, such as needle-free technologies and transdermal patches.
2. Global Vaccine Access: Efforts aim to ensure equitable access to vaccines worldwide.

Conclusion:

Immunization is a crucial public health strategy that prevents and controls the spread of infectious diseases by stimulating the immune system to produce protective antibodies. It encompasses various vaccine types, including live attenuated, inactivated, and subunit vaccines. Immunization prevents disease, promotes herd immunity, and has led to the eradication and reduction of many dangerous infections. Vaccine development involves antigen selection, clinical trials, and post-marketing surveillance.

Immunization schedules and booster doses ensure long-lasting protection. Ongoing research explores innovative vaccine delivery methods and global vaccine access. Medical professionals play a pivotal role in educating the public, administering vaccines, and contributing to the advancement of immunization strategies that protect individuals and communities from vaccine-preventable diseases.

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