Principles of Immunization

By

Dr. Oluwaseyi Israel

Dept. of Community MedicineBowen Univ. Teaching Hospital, Ogbomoso

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Outline

• Introduction

• Expanded Programme on Immunization (EPI)

• National Programme on Immunization (NPI)

• Principles of Immunization

• Adverse Event Following Immunization (AEFI)

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Introduction

• Immunization:

• Is a process where by a person is made immune or resistant to an infection through the production of antibodies, in response to the administration of vaccines

• It is the most powerful, cost-effective means of preventing some of the deadly childhood diseases

• It is a proven tool for controlling, elimination and eradication of life-threatening infectious disease

• It is one of the components of primary health care

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Expanded Programme on Immunization (EPI)

• The Expended program on Immunization is a world Health Organization Program with the goal to make vaccines available to all children throughout the world

• “Expanded” means:

• Expanding the number of diseases to be covered

• Expanding the number of children and target population to be covered

• Expanding coverage to all corners of the country and spreading services to reach the less privileged sectors of the society

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Expanded Programme on Immunization (EPI)

• Experience with smallpox eradication program showed the world that immunization was the most powerful and cost- effective weapon against vaccine preventable diseases

• In 1974, the WHO launched its “ Expanded program on immunization” (EPI) against six most common preventable diseases (diphtheria, pertussis, tetanus, polio, tuberculosis and measles)

• The Expanded Programme on Immunization (EPI) was established in 1974 through a World Health Assembly resolution to build on the success of the global smallpox eradication programme, and to ensure that all children in all countries benefited from life-saving vaccines

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The Objectives of EPI

1. To increase coverage of immunization for eligible children

2. To reduce the incidence of immunizable diseases among children below five years of age

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Expanded Programme on Immunization (EPI)

• EPI was adopted/launched by Nigeria in 1979

• EPI took off fully in Nigeria in 1980

• EPI successfully attained the universal child immunization target of 80% by 1990 in Nigeria as in many countries

• Unfortunately, this coverage could not be sustained and there was a decline in the coverage and increase in the number of reported cases of the target diseases

• As a way of reawakening national consciousness and demonstrating ownership of the programme, the Nigerian govt in 1996 renamed the EPI as National Progrmme on Immunization (NPI)

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National Programme on Immunization (NPI)

• NPI was established as a parastatal under the FMOH, and became fully operational in 1998

• NPI works to protect Nigerian children against numerous fatal childhood diseases through vaccinations and education

• NPI aims for complete immunization against tuberculosis, hepatitis B, poliomyelitis, diphtheria, tetanus, whooping cough, measles, and yellow fever among other diseases , in the first year of life

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Principles of Immunization

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The immune system

• Immunity: Ability of an organism to recognize and defend itself against specific pathogens or antigens

• Immune Response: Involves production of antibodies and generation of specialized lymphocytes against specific antigens

• Antigen: Molecules from a pathogen or foreign organism that provoke a specific immune response

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Types of Immunization

• Active immunization:

• Resistance developed in response to stimulus by an antigen (infecting agent or vaccine) and is characterized by the production of antibodies by the host

• Passive immunization:

• Immunity conferred by an antibody produced in another host. It may be acquired naturally or artificially (through an antibody-containing preparation)

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Active Immunization

• Active immunization is the administration of vaccines containing microbial products with or without adjuvants in order to obtain long term immunological protection against the offending microbe

• Adjuvant is a substance that enhances the body’s immune response to an antigen

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Passive immunization

• Passive immunization is the administration of preformed antibodies either intravenously or intramuscularly

• It is used to provide rapid protection in certain infections such as tetanus or in the event of accidental exposure to certain pathogens such as hepatitis B

• It is also used to provide protection in immune compromised individuals

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Passive ImmunizationInfection Source of Antiserum Indications

Tetanus Immune human; horse Post exposure (plus vaccine)

Diptheria Horse Post-exposure

Gas gangrene Horse Post-exposure

Botulism Horse Post-exposure

Varicella-Zoster Immune human Post-exposure in immunodeficiency

Rabies Immune human Post exposure (plus vaccine)

Hepatitis B Immune human Post-exposure prophylaxis

Hepatitis A Pooled human Ig Prophylaxis

Measles Immune human Prophylaxis

Snakebite Horse Post-bite

Some autoimmune disease Pooled human ig Acute thrombocytopenia and neutropenia

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Types of Immunity

• Innate or natural Immunity:

• Immunity an organism is born with

• Acquired Immunity:

• Immunity that an organism develops during lifetime

• May be acquired naturally or artificially

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Types of Acquired Immunity

• Naturally Acquired Immunity: Obtained in the course of daily life.

• Two types:-

A. Naturally Acquired Active Immunity:

• Antigens or pathogens enter body naturally.

• Body generates an immune response to antigens

B. Naturally Acquired Passive Immunity:

• Antibodies pass from mother to fetus via placenta or breast feeding .

• No immune response to antigens.

• Immunity is usually short-lived (weeks to months).

• Protection until child’s immune system develops.22

Types of Acquired Immunity

• Artificially Acquired Immunity: Obtained by receiving a vaccine or antibodies.

1. Artificially Acquired Active Immunity: • Antigens are introduced in vaccines (immunization) • Body generates an immune response to antigens

2. Artificially Acquired Passive Immunity: • Antibodies are introduced into body by injection

• Snake antivenom injection from horses or rabbits.

• Immunity is short lived (half life three weeks)• Host immune system does not respond to antigens

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What is a Vaccine?

• A vaccine is an immuno-biological substance designed to produce specific protection against a given disease

• A vaccine is a non-pathogenic antigen that mimics a particular pathogen in order to elicit an immune response as if that actual pathogen were in the body

• Vaccination is a method of giving antigen to stimulate the immune response through active immunization (i.e. production of antibodies in the body to fight the antigens)

• A vaccine is antigenic or immunogic but not “pathogenic”

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What is a Vaccine?

• Vaccines are made from:

• Live micro-organisms that have been ‘treated’ so that they are weakened (attenuated) and are unable to cause disease

• Dead micro-organisms (killed vaccine)

• Some part or product of the micro-organism that can produce an immune response

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Types of vaccines

• Live vaccines

• Attenuated live vaccines

• Inactivated (killed vaccines)

• Toxoids

• Polysaccharide and polypeptide (cellular fraction) vaccines

• Surface antigen (recombinant) vaccines

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Types of vaccines

• Live vaccines

• Live vaccines are made from live infectious agents without any amendment

• The only live vaccine is “Variola” small pox vaccine, made of live vaccinia cow-pox virus which is not pathogenic but antigenic, giving cross immunity for variola.

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Types of vaccines

• Live attenuated (avirulent) vaccines• Is a vaccine produced by reducing the virulence of a pathogen, but still

keeping it viable (or alive)• Attenuation takes an infectious agent and alters it so that it becomes

harmless or less virulent• often confer lifelong immunity with only one or two doses• Live attenuated vaccines should not be administered to persons with

suppressed immune response :• Leukemia and lymphoma • Other malignancies• Immunocompromised patient e.g. HIV • Receiving corticosteroids and anti-metabolic agents • Radiation • Pregnancy

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Types of vaccines

• Inactivated (killed) vaccinesOrganisms are killed or inactivated by heat or chemicals but remain antigenic

• Most inactivated vaccines, however, stimulate a weaker immune system response than do live vaccines.

• So it would likely take several additional doses, or booster shots, to maintain a person’s immunity

• They are usually safe but less effective than live attenuated vaccines

• The only absolute contraindication to their administration is a severe local or general reaction to a previous dose

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Types of vaccines

• Toxoids: detoxyfied toxinThey are prepared by detoxifying the exotoxins of some bacteria rendering them antigenic but not pathogenic

• The antibodies produces in the body as a consequence of toxoid administration neutralize the toxic moiety produced during infection rather than act upon the organism itself

• In general toxoids are highly efficacious and safe immunizing agents

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Types of vaccines

• Polysaccharide and polypeptide (cellular fraction) vaccines

• They are prepared from extracted cellular fractions e.g.• meningococcal vaccine from the polysaccharide antigen of the cell wall

• the pneumococcal vaccine from the polysaccharide contained in the capsule of the organism

• Haemophilus influenzae type B vaccine and

• hepatitis B polypeptide vaccine

• Their efficacy and safety appear to be high

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Types of vaccines

• Surface antigen (recombinant) vaccines

• It is prepared by cloning HBsAg gene in yeast cells where it is expressed

• HBsAg produced is then used for vaccine preparations

• Their efficacy and safety also appear to be high

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Principles of Vaccination

• The primary goal in vaccination is to provide protective immunity by inducing a memory response to an infectious microorganism using a non-toxic antigen preparation

• Antibodies produced as a result of immunization are effective primarily against extracellular organisms and their products e.g., toxins. Passively administered antibodies have the same effect as induced antibodies

• The ultimate goal of any immunization program is the eradication of the disease

• This requires that the infection is limited only to humans, with no animal or environmental reservoir, and the absence of any subclinical or carrier state in humans

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Principles of Vaccination

• Achieving elimination requires a high level of herd immunity to prevent person to person spread

• This requires considerable infrastructure support to ensure that all at-risk populations are targeted for immunization

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Herd Immunity

• Resistance to the spread of an infectious disease within a population that is based on pre-existing immunity of a high proportion of individuals as a result of previous infection or vaccination

• Herd immunity is a form of indirect protection from infectious disease that can occur with some diseases when a sufficient percentage of a population has become immune to an infection, whether through vaccination or previous infections, thereby reducing the likelihood of infection for individual who lack immunity

• Heard immunity is achieved when a sufficient portion of a population is simultaneously immuned to prevent sustained transmission

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Routes of administration

• Oral route (Polio vaccine, oral BCG vaccine)

• Intradermal route (BCG vaccine)

• Deep subcutaneous or intramuscular route (most vaccines)

• Scarification (small pox vaccine)

• Intranasal route (live attenuated influenza vaccine)

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Adverse Event Following Immunization (AEFI)

• An AEFI is any untoward medical occurrence which follows immunization and which does not necessarily have a causal relationship with the usage of the vaccine

• The adverse event may be any unfavorable or unintended sign, abnormal laboratory finding, symptom or disease

• There is no vaccine that is 100% safe without any risks

• Such events may range from mild side effects to life threatening

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Classification of AEFIs

• Vaccine product- related reaction: • An AEFI that is caused or precipitated by a vaccine due to one or more of the

inherent properties of the vaccine product

• Vaccine quality defect-related reaction: • An AEFI that is caused or precipitated by a vaccine that is due to one or more

quality defects of the vaccine product including its administration device as provided by the manufacturer

• Immunization error-related reaction: • An AEFI that is caused by Inappropriate vaccine handling, prescribing or

administration

• Immunization anxiety-related reaction: • An AEFI arising from anxiety about the immunization

• Coincidental event: • An AEFI that is caused by something other than the vaccine product,

immunization error or immunization anxiety41

Classification of AEFIs

• Vaccine product- related reaction: • EXAMPLE Extensive limb swelling following DTP vaccination

• Vaccine quality defect-related reaction: • EXAMPLE Failure by the manufacturer to completely inactivate a lot of

inactivated polio vaccine leads to cases of paralytic polio

• Immunization error-related reaction: • EXAMPLE Transmission of infection by contaminated multidose vial

• Immunization anxiety-related reaction: • EXAMPLE Vasovagal syncope in an adolescent following vaccination

• Coincidental event: • EXAMPLE A fever after vaccination (temporal association) and malarial

parasite isolated from blood42

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Vaccine Reactions

• Two types of vaccine reactions: • Minor and Severe

• Minor Reactions:

• Usually occur within few hours of injection

• Resolve after short period of time and pose little danger

• Local (includes pain, swelling or redness at injection sites)

• Systemic (includes fever, malaise, muscle pain, headache, loss of appetite)

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Vaccine Reactions

• Severe/Serious reactions:

• Can be disabling

• May require hospitalization

• May be life threatening

• E.g. Seizures, allergic reactions, anaphylactic shock, death

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Vaccine Safety Terminology: Cluster

• A cluster of AEFIs is two or more cases of the same adverse event related in time, place or vaccine administered

• Any AEFI that is of concern to the parents or to the health care worker should be notified

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Contraindications to vaccination

• Absolute contraindications (applicable to all vaccines): • Anaphylaxis following a previous dose of the relevant vaccine

• Contraindications applicable to live (parenteral and oral) vaccines:• Live vaccines should not be administered to persons who are significantly

immunocompromised, regardless of whether the immunocompromise is caused by disease or treatment

• In general, live vaccines should not be administered during pregnancy,

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Causes of Vaccine failure

• Vaccine:• Failure of the cold chain• Expired vaccine

• Health worker:• Wrong formulation of vaccine • Error in vaccine administration• Wrong dosage• Wrong site of administration

• Host factors

• Host immunity – immunocompromised patient, comorbidities etc

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Questions and Answer

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Thanks for your attention

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