IMMUNIZATION IN PEDIATRIC PATIENTS

IMMUNITY

The term immunity refers to resistance exhibited by the

host towards injury caused by microorganisms and their

products.

Protection against infectious or pathogenetic agents is

only one consequences of immune response, which in

entirely is concerned with reactions of body against any

foreign antibody. Immunity hence by different mates plays a

significant role in normal life of an individual without which

survival is almost compromised.

Study of immunity has a long history where in 1718

(18 t h century) people used small pox infectious sites for

inoculation in their children at an early age. This proved

very much successful by preventing further attack of small

pox in children at on older age. This began the process or

method of immunization of children so as to prevent further

attacks from a similar organism.

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Types of immunity:

Immunity against infectious agents is of different types

namely:

1. Innate immunity:

a) Specific Species

Racial

b) Non specific Individual

2. Acquired immunity:

Acute Natural

Artificial

Passive Natural

Artificial

Innate immunity:

Innate immunity or native immunity of an individual is

the immunity, which an individual possesses by virtue of his

genetic and constitutional make up.

It does not depend upon the caries contact of an

individuals with infectious agents or immunization.

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It may be non-specific when the degree of resistance to

an infection is considered in general or specific when

resistance to a particular pathogen is concerned.

Innate immunity is considered at the level of species,

race and individual.

Immunity at the level of species is shown by total or

relative refractoriness to a pathogen shown by all individuals

of a species. For example, human beings are resistant to

infections from plant pathogens and to pathogens of animals.

The mechanism of this immunity is not understood

fully but may be due to changes in physiological and

biochemical properties between tissues of different host

species which determines whether or not the pathogen can

grown in them.

Racial immunity is evidenced by differences in total

resistance capacities of individuals of different races. It can

be seen mainly in animals. In human beings it is seen that

the overall resistance of negroes is more when compared to

whites. Infections like malaria are more frequently in whites

when compared to negroes possibly because, the high

incidence of sickling (sickle cell carcinoma) provides

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resistance against malaria organisms. Each racial differences

are known to be genetic in origin and by selection and in

breeding possible to develop at will races that have higher

degree of resistance or susceptibility to various disease

pathogens.

Immunity (innate) at individual level can be considered

under various aspects as follows:

1. Age: Two extremes of life present with increased

susceptibility to infections. The immune system

in children is weak as it is still in a developing

stage. In fatal life infections are reduced by

immune system of mother. In younger age

increased susceptibility may be due to hormonal

alterations. As the age is progressed towards old

age the immune system gets waned and again

susceptibility to infections is increased.

Hormonal Influences:

Endocrine disturbances like diabetes, adrenal

dysfunction, hypothyroidism etc are activated with enhanced

susceptibility to infections. In all these cases immune

mechanisms are compromised. The corticosteroids suppress

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immune system by their action as anti-inflammatory and

antiphagocytic. At the same time steroids also exhibit

properties like neutralization of bacterial endotoxins.

Nutrition:

The relation between nutrition and immunity very

complex. In general both cell mediated and humoral

immunity are reduced in malnutrition.

It is also seen that certain conditions may not be seen

in severely ill patients. The malarial infection in very severe

illness may not induce fever but when diet (nutrition) is

improved it may produce fever. It is found hence that certain

viruses and bacterias can not grow in cases of severe illness.

Mechanism of Innate Immunity:

Skin and mucous membrane:

An intact skin and mucous membrane provide

considerable protection against invasion by microorganisms.

Healthy skin possesses bactericidal property by means

of high concentration of salt in drying, sweat. The sabecious

glands and long chained free fatty acidic also impart a

protective action against microorganisms.

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Mucosa of respiratory tract has several innate

mechanisms to provide immunity. Before the air could enter

the lungs starting from the point of entry of air into nasal

orifices the air is filtered to remove all impurities, the larger

particles are removed in nasal cavity by ciliac and mucous

secretions. The smaller particles which escape from nasal

cavity are removed by mucous secreted along the bronchus.

Once the particles are caught they are ultimately coughed

out. Any other small particles escaped through these ways

are removed by phagocytes in respiratory alveoli.

Mouth is constantly bathed by saliva which has several

antibacterial properties. The particles in mouth are subjected

to various digestive juices and ultimately digested. Strong

acidic pH in stomach helps in fighting against many

organisms. If organisms can survive in acidic environment

these are ultimately killed in intestine when the pH of

secretions increases gradually and becomes alkaline.

Intestinal mucosa consists of normal microbial flora

which prevents further colonization by other organisms.

Conjunctiva is freed from foreign particles by the

flushing action of lacrimal secretions. Tears contain

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lysozymes, an antibacterial substance in them. This lysozyme

is in an amount present in lacrimal fluid mainly active

against gm positive non pathologic cocci, lysozymes are

present in all of the tissue fluids and secretions except in

C.S.F. sweat and urine. It has been found that phagocytic

cells contain significant amounts of lysozyme in them to be

active against majority of athogenic organisms.

Flushing action of urine frees the bacteria from

urethra.

Antibacterial substances in blood and tissues:

Complement system possesses bactericidal properties

and plays an important role in destruction of pathogenic

organisms that invade blood and tissues. Propordin a

substance present in normal serum combines with

complement an mg++ ions lysis of gm negative bacteria and

also some viruses.

Several other factors having antibacterial property in

blood are:

1. Beta lysine – A relatively hemostable substancec active

against anthrax and related bacilli.

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2. Basic polypeptides like lukins secreted from

leukocytes and plakin secreted by platelets.

3. Lactic acid in muscles and in inflammatory zones.

All these substances exhibit antibacterial properties.

Cellular factors in Innate Immunity:

Natural defence against invasion of blood and tissues

by microorganisms and other foreign particles is mediated to

a larger extent by phagocytic cells, which ingest and destroy

them.

Phagocytic cells are classified as microphages and

macrophages. The microphages consist of

polymorphonuclear leukocytes. Macrophages consist of

wandering ameboid cells. Cells of reticuloendothelial system

and monocytes.

A major function of RE system is removal of foreign

particles that enter the body. The phagocytes reach the site

of inflammation by different chemotactic substances and

ingest the foreign bodies. The bacterias are phagocytosed

into a vacuole which combines with lysosyme to form

phagolysosome. The phagolysosome is subjected to various

lytic enzymes to destroy the organism.

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Inflammation:

Tissues injury or irritation initiated by the entry of

microorganisms leads to inflammation which is an important

nonspecific defense mechanism. The blood vessels constrict

initially followed by dilatation. The processes like

margination ad diapedesis and emigration of leukocytes from

blood vessels to inflammatory site takes place which leads to

phagocytosis.

Fever an increase in overall body temperature is also a

defense mechanism mainly by inhibiting in growth or

destroying pathogenic organisms.

Acquired Immunity:

The resistance that is acquired during life of an

individual is known as acquired immunity. It is different

from innate immunity which is inborn.

Acquired immunity is of two types namely:

1. Active immunity.

2. Passive immunity.

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Active immunity:

Active immunity is the resistance developed by an

individual as a result of an antigenic stimulus. This involves

active functioning of persons immune system leading to

synthesis of antibodies and / or immunologically active cells.

Active immunity sets in only after a latent period

which is required for the immunologic machinery to set in

motion. During the development of active immunity there is

often a negative phase during which, the measurable

immunity is lower than the immunity present prior to

exposure to an antigen.

This is seen because, during the process or period of

initial exposure, the antibodies normally present are utilized

for phagocytosis and therefore there is a net reduction in

total immunity. Once the immunity sets in it increases

rapidly and remains for a longer period of time. A second

similar exposure leads to setting of immunologic response at

a very faster rate and more efficiently.

Active immunity is characterized by immunologic

memory. This means memory of prior antigenic exposure is

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retained for a longer period of time and produces a

secondary type of reaction when it meets same antigen.

(Active immunity is more effective and confers better

protection than passive immunization).

Passive Immunity:

The resistance that is transmitted in a readymade form

is known as passive immunity.

The host immune system plays no role in providing

protection. The antigenic stimulus is absent, instead,

preformed antibodies are administration. Unlike active

immunity, the latent period is absent. The immune actions

begins almost immediately and the negative phase is absent.

The immune reaction is transient and lasts for few

weeks to months. This protection is seen till the passively

administered antibodies are metabolized and eliminated from

the body. No secondary type of reaction is seen. Instead if

the same antibody is given again for the second time it is

eliminated more rapidly from the body when compared to

first time. This factor of immune elimination limits the

usefulness of passive immunity.

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The passive immunity is therefore less useful than

active immunity in providing immune capacity. The only

advantage being its immediate action.

Active Immunity Classification:

Active immunity may be:

- Natural

- Artificial

Natural active immunity results from either clinical or

inapparent infection from a parasite.

A person who has recovered from these infections

develops natural active immunity. Example, a person

recovered from small pox, chicken pox etc.

Increased resistance to poliomyelitis in individuals of

developing countries due to many subclinical attacks by

poliovirys in childhood.

Some viral infections may give life long immunity

(measles).

The period of natural active immunity varies from the

type of pathogen and virulence of pathogens. Some viral

infections like common cold due to influenza virus may give

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only a shorter period of immunity. The common cold due to

influenza virus may recur due to reduction in immune

response to second infection.

The immunity following bacterial infection is less

permanent when compared to viral infection some infections

like typhoid fever provide sufficient immunity for a longer

period of time.

A special type of immunity called premunition is seen

in syphilis. This is characterized by presence of immunity to

a pathogen is seen as long as the original infection is active.

Once the original infection is cured, the person becomes

susceptible to infection by the same microorganisms again.

Artificial Active Immunity:

Immunity in children includes involves both natural

active immunity and artificial active immunity.

The artificial active immunity is the immunity or

resistance induced by vaccine. Vaccine are the preparations

of live or killed microorganisms or their products used for

immunization.

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The vaccine therefore are divided in to:

1. Live vaccine Bacterial

Viral

2. Killed Bacterial

Viral

3. Bacterial products divided vaccine – toxoids for

diphtheria and tetanus.

Live vaccines initiate on infection without causing any

injury or disease. The immunity following live vaccine

administration is similar to that following natural infection

but is of a lower order.

Once set, the immunity lasts for several years, but

booster doses are / may be necessary.

The administration of live vaccine in children /adults

may be done orally, (example – sabin vaccine and

poliomyelitis or parentrally. Example, Smallpox virus

vaccine.

Killed vaccine are generally less immunigenic than live

vaccine and the protection by them lasts only for a shorter

period of time. Therefore they require to be administered

repeatedly, usually at least two times. The first injection is

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known as primary dose and second dose is known as booster

dose.

killed vaccine can be again given either orally (taboral

vaccine for typhoid) or parenterally. The oral route is

generally not as effective as by parental route.

The killed vaccine by parental route generally provide

humoral antibody response.

Not all the organisms are available in avirulent form.

In order to overcome this if living organisms are to be

present in vaccine (live vaccine) they have to be treated in

such a way that the organisms loose their disease producing

ability. This process is called as attenuation.

The commonly used methods for this include adopting

the organisms to unusual environmental condition so that

they lose the ability to replicate completely in their usual

host. Culturing the viruses at a temperature lower than

normal is the next method.

Live attenuated vaccine provoke a rapid protective

response through stimulation of interfering production.

Live vaccine are difficult and expensive to prepare,

possibility of dangerous extraneous organisms is also seen.

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Natural Passive Immunity:

Natural passive immunity is the resistance passively

transferred from the mother to infant /baby. In humans

maternal antibodies are predominantly transferred through

placenta (especially IgG) and gives immunity to the infant,

human chelostrum is rich in IgA and also contribute for

immunity of the featus. From about 12 t h week of I.U. the

human embryo starts developing IgM in its body. But the

IgM embryo at this stage is not active enough to combat all

the infections.

It is only at about after 3 months post anterior life the

infant gets immune capacity independently. Till then the

child utilizes immune system of mother that is transmitted to

it.

The transmission of antibodies from maternal to factal

circulation across placenta is an active process and it is

found that fectus has more concentration of antibodies than

maternal circulation protection so afforded is sufficient to

resist all infections during that period. Hence any infections

are more common after 3 months of age.

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By active immunization of a pregnant women it is

possible to improve the passive immunity in infants.

The recommendation of titanus tunoid vaccine

prophylactically is hence of use in areus with increased

tendency for neonatal titanus.

Artificial Passive Immunity:

Artificial passive immunity is the resistance passively

transferred to a recipient by injecting antibodies. The agents

used for this purpose are hyper immune animal and human

sera, convalescent sera, and pooled human gamma globulin.

The oldest and commonest method employed is to inject

hyper immune horse sera. It is prepared by injecting

appropriate antigen into horse serum.

Example – Anti-tetanus serum (ATS) used for

prophylaxis against tetanus infection is prepared by

administering a series of doses of antigens into horse

circulation. Then the blood is collected and serum is

separated from blood. The antibodies are then concentrated

and purified and sterilized.

The main problem with animal enzymatic preparations

is an increased tendency for hypersensitivity reactions.

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In order to overcome this problem human sera can be

utilized.

Serum collected from patients convalescing from

infections diseases contain high concentration of specific

antibodies. Such convulsing serum is utilized for passive

immunization against viral infections like measles and

rubella.

The main risk of using human sera is transmission of

serum hepatitis.

Passive immunization is utilized mainly for providing

immediate and temporary protection in a non immune host

having chances of infection. It is also utilized to provide

resistance till active immunization is in action.

Passive immunization can also be employed with active

immunization and this is called as “combined immunization”.

Combined immunization is indicated whenever an immediate

action is required which is given by passive immunization.

The immune actions remains active after words by active

immunization.

Paediatric or childhood is the best age at which

majority of disease can be prevented by means of various

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methods. Vaccination in childhood has become an

inexpensive and most useful methods by which prophylaxis

can be given.

Since the time of introduction of vaccine there is a

decline or reduction in the overall rates of infections like

cholera, tuberculosis, typhoid, mumps, smallpox, tetanus and

polio etc. which are most common diseases affecting in early

childhood.

Some of the diseases against which the immunization

by vaccines is available at present are:

1. Diseases that can be prevented by environmental

improvement or vaccination:

- Japanese encephalitis.

- TB.

- Yellow fever.

- Typhoid.

- Rubis

- Cholera

- Hepatitis B (Horizontal transmission).

2. Diseases preventable only by vaccination:

- Poliomyelitis.

- Diphthories.

- Measles.

- Rubella.

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- Mumps.

- Purtysis.

- Meningococcal meningities.

- Influenza.

- Chickenpox.

- S.pneumonia pneumonia.

- Hepatitis B (vertical transmission).

Routine Vs Special Immunization:

Based on prevalence and severity of a disease, safe and

vaccine are preferred for routine repeated administration in

infants and early childhood. Thus in India routine

administration is recommended for:

- Measles.

- Diphthoria.

- Tetanus.

- Purtusis.

- Typhoid fever and

- Tb

Robis vaccine is usually given as a post exposure

prophylaxis and in more prone individuals as a pre exposure

prophylaxis cholera vaccine is recommended only as a

measure against epidemics.

In pediatric practice immunization should be given to

all susceptible individuals and this vaccine is usually taken

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at an individual level. Immunization can safely be given in

minor illness like diahhroea, URTI etc.

In order to control the vaccine preventable disease

WHO and member countries including India has established

on expanded programme on immunization.

Some of the Practical Aspects

1. There is no contraindication for concurrent

administration of multiple vaccines like DPT, OPU, or

MMR.

2. A lapse in schedule of immunization does not always

necessitate reinstitution of total course. If a second

hours of DPT or OPU is missed it is not necessary to

reinstitute the complete course.

3. If immunization scheme of a child is unknown there is

no harm in giving appropriate vaccines again.

4. Dose reduction is not appropriate since it may cause in

appropriate immunologic response, increased dose is

also not indicated which may cause side effects.

5. Live vaccines of all types and BCG should not be given

in individuals with congenital disorders of immune

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system. These should also be avoided in children who

are taking steroids for rt since these causes

immunodepression. A short course of low dose of

steroids is not a contraindication for vaccines.

Vaccines of this kind should also be avoided in

children with active symptoms of AIDS.

6. Children suffering from neurologic disorders or with

previous history of convulsions are at a higher risk for

purtuse vaccine.

7. Active immunization after exposure to disease is

indicated in:

- Rabies.

- Measles (within 3 days of exposure).

- Hepatitis and

- Tetanus.

Immunization schedule:

Various immunization schedules are recommended in

order to protect a child from infections. Some of the

immunization schedules are:

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National Immunization schedule :

The first visit may be made when the child is 6 weeks

old. The recommended schedule is given in next page.

Beneficiaries Age Vaccine No. of doses

Route of administration

Infants6 weeks

to 9 months

DPT

POLIO

BCG

3

3

1*

Im

Oral

Intradermal

9-12 months Measles Subcutaneous

Children 16-24 months

DPT

Polio

1*

1**

Im

Oral

5-6 years

DT

Typhoid

1@

2

Im

Subcutaneous

10 yearsTetanus tonoid

Typhoid

1@

1@

Im

Subcutaneous

16 yearsTetanus T

Typhoid

1@

1@

SC

SC

Pregnant women

16-36 months T-T 1@ Im

* For institutional deliveries BCG should be given at birth.

** Booster dose

@ 2 doses if not vaccinated

1 Intervals between two doses should not be less than one month

2 minor illness is not a contraindication.

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WHO EPI schedule

This strongly recommended institution of BCG and

polio vaccines at birth or at the time of initial contact, in

countries where Tb and polio have not been controlled. In all

countries immunization for polio is safely started at 6 weeks

of age along with DPT.

The given schedule is as follows:

Age Vaccine

Birth BCG, oral polio

6 weeks DPT, oral polio

10 weeks DPT, oral polio

14 weeks DPT, oral polio

9 months Measles

Diphtheria:

Common disease in India, which has sufficient number

of antibodies circulating in maternal circulation. The

antibodies are easily to crossed across placenta and fetal

immunity is cortered till birth and for first 3 months.

The vaccine is given as a triple vaccine DPT or D.T.

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Primary dose consists of 3 doses at 4, 6 and 8 weeks of

birth, I booster dose is given during second year of age, at

18 months. A second booster dose is given at 5 years of life.

Pertusis:

- Given as triple vaccine DPT.

- Since protective antibodies cannot cross placenta

vaccination is a must.

- 3 doses are recommended at 9-8 weeks of internal from

1-3 months of age.

- Common adv reactions:

o Local pain irritability.

o Screming for a prolonged time.

o Convulsions in some cases.

- Not recommended in neuromuscular disorder and

patients with convulsive history.

Tetanus:

- Neonatal tetanus is an important cause of mortality in

many developing countries.

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- Since there is no natural immunity, the unimmunized

mothers fail to transfer the antibodies to their infants

against tetanus toxin.

- Immunizing pregnant women with T toxoid of great

value.

- Vaccination against TT is given as DPT or DT or TT

alone.

- Booster dose is given at 18 months, 5 years and 10

years and thereafter 6 months intervals.

BCG:

- Bacillus culmette guerin is an attenuated strain of

mucobacterium tuberculosis. It is a line vaccine.

- In order to maintain its potency the vaccine is supplied

at a temperature of 4°C at which the potency remains

satisfactory for several months.

Since no immunity is transferred from mother to infant

BCG has to be administered after birth. The vaccine is given

intradermally above the deltoid muscle. After 2-3 weeks a

papule develops at the site of injection which ultimately

heals by scarring.

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Adverse reaction being

- Regional lymphnods with infrequent dressing.

Measles:

- Live attenuated measles virus is used as a vaccine.

- Vaccine stored at 4-8°C can be used for 1 year.

- Given by S.C. or Im route.

- Recommended minimum age is nine months. Because

before this period maternal antibodies circulating in

fetal blood neutralizes the virus in live vaccine.

Mumps:

- Vaccine consists of live attenuated mumps.

- Given as a trivalent vaccine with measles and rybella.

- Mumps vaccine of MMP may be given after 12-15

months of age.

Rubella:

- Immunization is given solely to prevent congenital

rubella.

- Two approaches are recommended.

o Either to selectively immunize girls.

o Immunize girls and boys simultaneously.

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- In India incidence of rubella is not known.

- Prophylaxis starts at on age of 12 months.

Rabies:

- Cause (explain).

- Since the incubation period is more post exposure

vaccination is safely given for infected individual.

- It employs administration of killed rabies virus

vaccine.

- Modified semple’s vaccine is one vaccin for rabies

administered S.C. over anterior abdominal wall for 7-

14 days. In some cases booster doses are also required.

- Modern vaccine have advantage over semples vaccines

in that no neurological symptoms are seen.

- These vaccine are given Im or Sc on 0, 3, 7, 14, 30 and

90 days.

Typhoid:

- Employs standard acetone killed salmonelle typhi

infections.

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- Primary immunization requires two S.C. doses at 4

week intervals. In out breaks the period may be

reduced to 1 week also.

- Dose is 5ml for children of 10 years.

- Booster doses once in 3 years are recommended.

Cholera:

- Suspension of heat killed vibrio cholera is used as

vaccine for cholera.

- Recommended rarely and only in outbreaks of the

disease.

- Given either ID, Im or Scly.

Hepatitis B

A purified suspension of 22 nanometer particles

bearing H.B. virus surface antigens found in some chronic

carriers are used as vaccines. Any residual virus is

inactivated by formaldehyde and heat.

Recently a genetically engineered recombinant vaccine

is available.

In pediatrics its main use is in preventing mother to

transmit the disease to infant neonates borned to carrier

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mothers should given Human anti hepatitis B globulin

(AHBG) and a course of vaccines according to

recommendation by manufacturers.

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