OIA1010 IMMUNIZATION AND VACCINATION

Immunization (Vaccination)

Confers protection against infectious diseases

Achieved through administration of pathogen or it's toxin which altered that they lost their pathogenicity but retained antigenicity

Generate protection prior to possible exposure to infectious agents

Principles

Based on specificity & memory in acquired immune system

Memory cells allow immune system to mount stronger response on second encounter with the antigen. Second response both faster and more effective than primary response (often too slow to prevent disease)

Concept of Immunity

Self vs. Non-self

Antigen specificity

Indicated by presence of effector cells

Protection from infectious diseases by various methods

Primary Response

At lag phase, antigen recognised as "foreign" and cells proliferate & differentiate in response to antigen. Usually 5 to 7 days.

At log phase, antibody concentration increases exponentially as B cells stimulated by antigen and differentiate into plasma cells which secretes antibodies.

At plateu/ steady-state phase, antibody synthesis balanced by antibody decay, no net increase in antibody concentration.

Secondary Response

Much shorter lag phase than primary response.

More rapid log phase and higher antibody levels achieved.

After steady-state phase, decline in concentration less rapid and antibody persists longer, may even lifetime.

Type of Immunization

Passive immunization

(Natural - transplacental, breast milk; Artificial - Human Immunoglobulin)

Include natural maternal antibodies, antitoxins & immune globulins

Protection transferred from another person or animal

Temporary immunity as immune system is not triggered, thus no presence of memory cells

Conditons Warrnting Passive Immunization

Deficiency in synthesis of antibodies due to congenital or acquired B-cells defect

Susceptible exposure to disease causing immediate complications

Disease already present

Active Immunization

(Natural - Infection; Artificial - Vaccination)

Include natural infection, vaccination and toxoids

Stimulate proliferation of T and B cells, resulting in formation of effector and memory cells -> Relatively permanent immunity

Type of Vaccines

Whole-Organism Vaccines

Many common vaccines consists of inactivated or attenuated bacterial cells or viral particles (attenuated & inactivated vaccines)

Attenuation & Inactivation Vaccine

Attenuation Viral or Bacterial Vaccine (weaken pathogens)

Live virus that are weakened and non-pathogenic but retain antigenicity that triggers strong cellular and antidboy responses -> lifelong immunity

Increase IgA response despite relying cell-mediated immunity

Achieved by growth under abnormal culture condition (risks of live microbe to mutate to virulent form)

E.g., Bacillus Calmette-Guerin (BCG) against TB, virus against yellow fever, polio and measles, mumps & rubella (MMR)

Inactivation Viral or Bacterial Vaccine (killed pathogens)

Whole virus treated: lost pathogenicity but retain antigenicity - emphasis humoral immunity activation

Disease causing microbes killed with chemicals, heat or radiation - lost replication ability (cannot mutate)

More safe and stable compared to live vaccines but result weaker stimulus to immune system -> requires booster dose

E.g., vaccines against polio, rabies, hepatitis A and bacteria causing pertussis

*Difficult to inactive due to potential for denaturation of epitopes (lost antigenicity)

Toxoid vaccines (Bacterial toxin causing disease)

Bacterial toxins treated: denature protein -> not dangerous but retain antigenicity and elicit protective antibodies

Toxoids activate immune system to produce antibodies that capable of binding and blocking interaction of natural toxin with specific receptor sites

E.g., Tetanus (Clostridium tetani) & Diphtheria toxoids (Corynebacterium diphtheriae)

Conjugate vaccines

Children < 2 years: generally unable to respond to T-cell independent antigens (e.g., bacterial capsular polysaccharides)

Polysaccharides conjugated to T-dependent antigens (e.g., diphtheria & tetanus) that can be recognised

Special type of subunit vaccine

E.g., Hib vaccine (Hemophilus influenza type B)

Subunits vaccines

Only contain essential antigens that stimulate immune system the best

Reduced risks of adverse reactions with vaccines

Development: hard & time consuming

E.g., Hepatitis B surface antigens, bacteria caspular polysaccharides of S. pneumoniae, N. meningitidis and H. influenza.

Effectiveness of Vaccination (small percentage respond poorly)

Anti-vaxxer (Andrew Wakefield)

Linked between MMR administration and possible autism (Misconduct)

Falsifying data to misled readers of belieiving direct impact of vaccine on autism

Herd Immunity

Majority of population is immune -> low chance of susceptible individual infected (e.g., measles epidemic)

Factors Affecting Herd Immunity

Environmental factors: crowded conditions & seasonal variations

Immune system strength

Infectiousness of Disease: greater risk of infection, higher percentage need of vaccine: chance infecting non-immunised low if enough people vaccinated

Lead to disappearance of disease (smallpox): no need vaccination

Vaccination Contraindications

Immunization should be postponed if significant acute illness or high fever (>38^C) Minor illnesses are not contraindications for vaccination

Immunocompromised individuals & pregnant women should not receive live vaccines unless risks of exposure outweighs theoretical risks of acquiring the disease.