GENERAL PRACTITIONERS' COLUMN

Guest Editor: Bhim S. Pandhi

Immunization in Practice - Clearing the Cobwebs

A. K. Dutta & Sanghamitra Ray

Received: 2 November 2012 /Accepted: 28 December 2012# Dr. K C Chaudhuri Foundation 2013

Abstract Vaccination is one of the most cost effectivemethods of prevention of diseases without even raising thesocioeconomic status of the community. Small pox eradica-tion from the world is the perfect example of the role ofmass vaccination of the entire community of the universe.India is feeling proud to be polio free for the last 1 y and it isexpected that the world would be polio free very soon. Themost important purpose of National immunization programof any country is to prevent deaths due to vaccine prevent-able diseases followed by severe disability and morbidity inthat order. Therefore keeping in view the above principle,Govt of India has included Baciilus Calmette Guerrin(BCG), Oral polio vaccine (OPV), Diphtheria, Pertussis &Tetanus (DPT), Measles, Hepatitis-B and now Hemophilusinfluenza type b (Hib) vaccines in the armamentarium of theNational schedule. Every child in the country should receivebasic vaccines as per Govt. of India schedule and is avail-able free of cost at all health centers in India.

Keywords Immunization . Vaccination schedule . Adversereaction to vaccines

AbbreviationsBCG Bacillus Calmette GuerinDTwP Diphtheria, Tetanus and whole cell PertussisDTaP Diphthetia, Tetanus and acellular PertussisTd Tetanus and reduced dose of diphtheriaTdap Tetanus and reduced dose of diphtheria and

reduced dose of acellular pertussisPCV Pneumococcal polysaccharide vaccine

IPV Injectable polio vaccineHib Hemophilus Influenzae bOPV Oral polio vaccineHep A Hepatitis AHep B Hepatitis BMMR Mumps, Measles and RubellaHPV Human papilloma virus

Introduction

Immunization is one of the strongest weapon that we have inthe fight against a host of childhood diseases and to reduce theunder five mortality of India. Vaccine preventable diseasestake a heavy toll of life especially in infants and children. In aWHO estimate about 2.1 million deaths globally occur due tovarious vaccine preventable diseases out of which 1.4 millionare under the age of 5 y [1, 2] Govt. of India recommends,under the National immunization schedule, to provide BCG,OPV, DPT, Measles, Hepatitis B and Hemophilus influenza b(in few states) to all infants. Routine immunization coveragein India is poor especially in certain states. The general prac-titioner is a key player in the Indian health system to ensurethat this coverage is improved. This article would cover im-portant practical aspects of immunization in children for prac-ticing general physicians and pediatricians.

General Principles of Vaccine Administration [3]

1. Hand hygiene—Proper hand washing before vaccineadministration and site preparation.

2. Needles and syringes should be disposable and prop-erly disposed after use.

3. Children may be restrained adequately if needed be-fore injection.

A. K. Dutta (*) : S. RayDepartment of Pediatrics, Lady Hardinge Medical Collegeand Associated Kalawati Saran, Children’s Hospital, New Delhi110001, Indiae-mail: drdutta@gmail.com

Indian J PediatrDOI 10.1007/s12098-012-0957-8

4. Different vaccines should not be mixed in the samesyringe and expiry dates should be checked.

5. One should thoroughly read the instructions leaflet forpreparation of the freeze dried vaccine, dose and thediluents to be used.

6. Ask for any allergic manifestations of any food, drugsor any other serious adverse events that had occurredafter use of any previous vaccine.

7. Prepare yourself with all resuscitation equipments in theimmunization clinic including emergency medications.

8. After administration of any vaccine ask the individual towait (sit or lie down) for 15min for any untoward events.

9. Vaccination can be given with mild illness like mildcough, mild fever, mild diarrhea etc.

10. Ask for any malignancy, immunodeficiency includingHIV.

Injection Technique and Position of the Child

A rapid plunge of the needle through the skin is needed topenetrate the skin after relaxation of the muscle to be injected.For deltoid muscle, flexion of the arm and for anterolateralthigh, some degree of internal rotation of thigh would help inrelaxation of the muscles. Infants should be placed in the lapof the parents and for a bigger child sitting at the edge of thetable hugging parents. The needle size and needle length areshown in Table 1.

Scheduling of Vaccination

Two or more inactivated vaccines can be safely administeredsimultaneously or at any interval between the doses. Howeverif two or more live vaccines are to be administered, then aninterval of 28 d are required. However the exception is during

pulse polio program when OPV is recommended to be givenat any interval.

Minimum Ages and Minimum Intervals BetweenVaccine Doses

BCG, OPV and hepatitis B vaccine can be administered atbirth. For DPT, Hib, Injectable polio vaccine (IPV) and Con-jugate pneumococcal vaccine, the minimum age of vaccina-tion is 6 wk.

Unknown Immunological Status

A general practitioner may frequently encounter childrenwith unknown immunological status. Only written docu-ments should be regarded as evidence of immunization.In general, a child with unknown or uncertain immuni-zation status should be considered disease susceptibleand vaccination should be initiated early as per thecurrent age.

Lapsed Immunization

A lapse in immunization schedule does not requirerestarting of the entire series from the start and onlyremaining doses need to be administered in the nextvisit irrespective of the duration of delay. However,certain vaccine if missed at a particular age and thechild’s visit takes place at an age when the vaccine isno longer indicated the next dose need not be given.E.g., last Rota virus vaccine dose cannot be given after32 wk of life. In case of unknown or uncertain immu-nization status, it is better to administer age appropriatevaccines.

Vaccination in Preterm and Low Birth Weight Babies

All medically stable preterm and low birth weightbabies can receive all vaccines according to chronolog-ical age with the exception of hepatitis-B vaccine.Hepatitis-B vaccine should not be given at birth to ababy weighing less than 2000 g at birth unless themother is hepatitis B surface antigen (HBsAg) positiveor of unknown status and additional three more dosesshould be given to these children. Babies born withweight <2000 g and mother’s HBsAg status negativeshould wait till the baby is 30 d of chronological ageand medically stable regardless of gestational age orbirth weight.

Table 1 Site and needle length for intramascular (IM) immunization

Age group Needle/length(inches/mm)

Injection site

Newborns

upto <2 mo 5/8 (16) Anterolateralthigh muscle

>2 mo–1 y 1 (25) do

Toddlers and children 1–1.25 (25–32) do

Adolescent and young adults

Female and male, wt <60 kg 5/8 (16) Deltoid muscle

Female wt 60–90 kg 1.5 (38) do

Female wt >90 kg 1.5 (38) do

Male wt 60–118 kg 1(25) do

Male wt >118 kg 1.5 (38) do

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Vaccination During Pregnancy

All live virus vaccines are contraindicated during pregnancy.Tetanus, reduced dose of diphtheria and acellular pertussis(Tdap), Tetanus & reduced dose of diphtheria (Td), Tetanustoxoid (TT), Rabies and inactivated influenza vaccine can besafely given to pregnancy. In addition Hepatitis-A, Hepatitis-B,meningococcal and Pneumococcal vaccine can be administeredif indicated. Yellow fever vaccine is a live attenuated vaccineand if journey to the endemic countries cannot be postponed ormosquito bite is unavoidable, then vaccine can be administered.Human papilloma virus (HPV) vaccine is not recommended tobe used in pregnancy although it is an inactivated vaccine sincethe adverse outcome in fetuses is not definitely known.

Vaccination in Immunocompromised Children

In general all live vaccines are contraindicated in severe prima-ry and secondary immunodeficiency syndromes. However theimmune response to some of the inactivated vaccines e.g., DPT,Hep-B, Hep-A, IPV, Hib, Pneumo, Meningo and Influenzavaccines are inadequate. In children when immunosuppressiontherapy is discontinued, an adequate response to vaccinesdevelops after 3 mo to 1 y of discontinuation. All children withprimary and secondary immunodeficiencies should receiveannual age dependent inactivated influenza vaccine.

In primary immunodeficiencies, measles and varicellavaccines should be considered for children with B-lymphocytes disorders. Most experts believe that in com-plement deficiencies and phagocytic disorders, live-virusvaccines can be safely given.

In secondary immune deficiency states usually live vac-cines are not recommended. However in HIV infection mea-sles, MMR and varicella vaccine can be administered if theCD-4 count is >15 % or greater than expected for age.

Patients on systemic corticosteroid therapy at a dose of>2 mg/kg/d for more than 2 wk should not receive any live-virus vaccine until corticosteroid therapy has been discontin-ued for 1 mo. If systemic corticosteroid therapy of >2 mg/kg/dhas been received for less than 2 wk then live virus vaccinecan be given after discontinuation of the therapy. Howeversome experts defer vaccination for 2 wk after stoppage of thetherapy. Patients receiving steroid in the form of inhaled,topical application or maintenance doses and low dosescan receive all live virus vaccines.

Immunization Schedule

Immunization schedule of a country depends upon epidemi-ology of the disease, availability of the vaccine, programmaticfeasibility of delivery of vaccine to the recipient and cost. In

general the primary objective of vaccination program is toreduce infant mortality followed by prevention of seriousdisabilities. Based on this principle WHO recommends vac-cination schedule for the member countries and individualcountries then finalize the schedule for the country (Table 2).

Indian academy of pediatrics committee on immunization(IAPCOI) has revised the immunization policy for the prac-ticing pediatricians in 2012 [5] (Table 3). According to thelatest guidelines there are only two categories of vaccine.First category is for routine use and second one is to be usedin special circumstances.

Recommended Vaccines for High Risk Groupsof Children (Vaccines Under Special Circumstances)

1. Influenza vaccine2. Meningococcal vaccine3. Japanese encephalitis vaccine4. Cholera vaccine5. Rabies vaccine6. Yellow fever vaccine7. Pneumococcal polysaccharide vaccine (PPSV23)

High Risk Categories of Children

1. Congenital or acquired immunodeficiency (includingHIV infection)

2. Chronic cardiac disease, pulmonary disease includ-ing asthma if treated with prolonged high dose oralcorticosteroids), hematological disease, renal disease

Table 2 National Immunization Schedule (NIS) for infants, childrenand pregnant women [4]

Age Vaccine

Birth BCG, OPV0

6 wk DTwP1, OPV1, HepB1a, Hib1a

10 wk DTwP2, OPV2, HepB2, Hib2

14 wk DTwP3, OPV3, HepB3, Hib3

9–12 mo Measles

16–24 mo DTwPB1, OPV4, MMRa

5–6 y DT

10 y TT

16 y TT

Pregnant women TT1 (early in pregnancy)

TT2 (1 mo later)

TT booster (if vaccinated in past 3 y)

9, 18, 24, 30, 36 mo Vitamin A

a Hep-B, MMR, Hib are available in some districts only

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(including nephritic syndrome), liver disease, diabe-tes mellitus

3. Patients on long term steroids, salicylate, immunosup-pressive or radiotherapy

4. Diabetes mellitus, Cerebrospinal fluid leak, Cochlearimplant, Malignancies

5. Functional or anatomical asplenia/hyposplenia6. During disease outbreaks7. Laboratory personnel and health care workers8. Travellers

Recommendation of Individual Vaccines in Practice

In general practice all vaccines recommended under univer-sal immunization schedule of Govt. of India should beadministered to all the children. However, there are manyother vaccines available in the private market which can beused as per the recommendations. In the following fewparagraphs important guidelines of individual vaccines aregiven which may be followed. These guidelines are basedon consensus statement of Indian Academy of Pediatricscommittee on immunization after an extensive review anddeliberations on individual vaccines [5–12].

BCG Vaccine

BCG is one of the oldest vaccines incorporated in the immu-nization schedule. It is a freeze dried vaccine to be dilutedwithnormal saline and given by intradermal injection in the leftdeltoid region. The efficacy of BCG in preventing adult typeof tuberculosis is negligible. However, it prevents the seriousform of the disease e.g., military and tubercular meningitis.BCG is to be given as early as possible after birth, preferablywithin first 15 d of life. The vaccine can be given upto the ageof 5 y if missed at the early age. The side effects of BCGvaccination, local ulceration and regional lymphadenopathy,rarely occur and are usually self limiting and do not needintervention most of the time.

Polio Vaccine

As the landmark of polio elimination has been achieved inIndia; IAPCOI has adopted the strategy of sequential vacci-nation with OPV and IPV. IPV is now in wider use as aprotective measure against VDPV and to replace OPV glob-ally. IAP suggests use of IPV at 6, 10, 14 wk followed by 2doses of OPVat 6 and 9 mo, booster of IPVat 15–18 mo andOPV at 5 y. IPV can be offered upto 5 y in total three doseswith 2 doses at 2 mo gap and third dose after 6 mo as a catch-up vaccination [6–8]. Since IPVadministered in EPI scheduleresults in suboptimal seroconversion according to studies, asupplemental dose is required at 15–18 mo. IPV is givenintramuscularly or subcutaneously and even as a componentof fixed combination vaccines. Birth dose of OPV is stillrecommended in high risk countries like India [4].

DTP

It is also known as triple vaccine. DTwP consists of toxoid ofdiphtheria (20–30Lf), tetanus (5–25Lf) and whole cell pertussisbacilli. Dose is 0.5 ml intra-muscularly. Important side effectsinclude fever, persistent crying, hypotonic hyporesponsive epi-sodes, seizures, encephalopathy and pertussis component isresponsible for most of these. DTwP is not recommended for

Table 3 IAP immunization timetable 2012 (Recommended vaccinefor routine use) [5]

Age Vaccine

At birth BCG

OPV0

Hep B 1

6 wk DTwP1/DTaP1

IPV1

Hib1

HepB2

PCV1

Rotavirus1

10 wk DTwP2/DTa2

IPV2

Hib 2

PCV 2

Rotavirus2

14 wk DTwP3/DTaP3

IPV3

Hib3

Rotavirus 3

PCV3

9 mo Measles

OPV2

12 mo Hep-A 1

15 mo MMR1

Varicella 1

PCV booster

16–18 mo DTwP B1DTaP B1

IPV B1

Hib B1

18 mo Hep-A 2

2 y Typhoid 1

4 ½–5 y DTwP B2/DTaP B2

OPV3

MMR2

Varicella 2

Typhoid 2

10–12 y Tdap/Td

HPV

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children more than 7-y-old. DTaP contains acellular pertussisvaccine and has got lesser side effects. Another form availablein India is Tdap (boostrix) which can be used in children morethan 7 y of age and even in adults. Children more than 7 y-oldwho are incompletely immunized with DTwP/DTaP can begiven 1 dose of Tdap and 2 doses of Td at 0, 1, 6 mo.

MMR

Contrary to the earlier belief, single dose of measles vaccinedoes not give lifelong immunity. Measles vaccine given asmonovalent vaccine at 9 mo of age has approximately 80–85 % protective efficacy and hence at 15 mo MMR vaccineis recommended which also protects against mumps andrubella. The immunity of measles vaccine wanes at 5 y ofage and hence one more dose is recommended at schoolentry. Catch up vaccination can be done in children with 2doses 4–8 wk apart with no upward age limit.

Hib

It is a conjugated vaccine administered in dosage of 0.5 mlintramuscularly. Available types include Hb-OC, PRP-T,PRP-OMP; among them the first 2 are available in India.Vaccination schedule includes 3 doses when started below6 mo, 2 doses between 6-12 mo, 1 dose between 12-15 mowith a booster dose at 18 mo.

Hepatitis A

It is an inactivated vaccine used as two doses 6 mo apart andrequires no booster. Live attenuated vaccine (Biovac) is alsoavailable in dosage of 1 ml subcutaneously in children 1–15 y.Live vaccine cannot be used as post-exposure prophylaxis.

Hepatitis B

It is a recombinant vaccine used in dosage of 0.5 ml (10 μg)in less than 18 y of children and 1 ml (20 μg) in olderchildren. Recommended schedule has been changed fromthe earlier 0, 1 and 6 mo schedule to 0, 6 wk, 6 mo. It is incontext of the latest ACIP (Advisory committee on immu-nization practices) recommendations [2] that the final thirdor fourth dose is to be given not earlier than 24 wk and aftera minimum gap of 16 wk after the first dose. In immuno-compromised children the vaccine should be administered at0, 1, 2 and 12 mo in double dose. Antibody titre of morethan 10 mU/ml is considered protective.

Typhoid Vaccine

Currently available vaccines are Vi-capsular polysaccharidevaccine and Vi-conjugate vaccine. IAP recommends Vi-

polysaccharide vaccine 0.5 ml intramuscularly every 3 y start-ing at the age of 2 y till 18 y. Those with history of enteric fevershould also receive this vaccine 4 wk after the recovery if theyare not is not vaccinated in last 3 y.

Pneumococcal Vaccine

This unconjugated polysaccharide is 23 valent (PPV 23). Twodoses are sufficient for lifetime protection. PPV23 can be usedin children 6 to 18 y who are immunocompromised with asecond dose after 5 y. It can be given in children of 2 y or moreand a gap of 2 mo should be maintained between PCV andPPV 23. Conjugated vaccines include PCV7 and PCV10 andPCV 13. Serotype coverage of all of the three vaccines wereanalysed but it was concluded that due to non-availability ofadequate data on the prevalence of different serotypes in India,it is not possible to determine the superiority of one vaccineover the other. But it has been estimated that these new PCVsconfers protection against almost 70 % [3] of the prevailingserotypes. Schedule for PCV include 3 doses at 6, 10, 14 wkand 1 booster at 15–18 mo.

Meningococcal Vaccine

Unconjugated polysaccharide vaccines are either bivalent orquadrivalent and indicated in children of more than 2 y. Con-jugated vaccine is preferred but is not available in India atpresent. It is recommended only for high risk children, duringan outbreak and in travellers. Only a single dose 0.5 mlsubcutaneously or intramuscularly is given. Revaccination isadvised only once after 3 y for those who are at high risk.

Human Papilloma Virus (HPV) Vaccine

Two vaccines are available—quadrivalent vaccine(Gardasil) and bivalent vaccine (Cervarix). Gardasil con-tains 4 serotypes of HPV 6,11,16,18 and is scheduled for 3doses at 0,2 and 6 mo. Cervarix contains HPV serotypes 16,18 with 3 doses at 0, 1 and 6 mo. Recommended age forvaccination is 10–12 y and permitted upto 26 y.

Rota Virus Vaccine

The incidence of rotavirus positivity amongst hospitalizedchildren varies from 6 % to 45 % (20.8 %) [4]. According toIndian surveillance study rota virus was responsible for entericinfection in almost 39 % of the study population [5]. Thoughthere is no population based efficacy trial of the available rotavirus vaccines in India, IAPCOI still recommends this vaccineas it can reduce the disease burden markedly in a country likeIndia with a high load of enteric infections despite a smalldefinite risk of intussuception. The committee also stressesthat while prescribing this vaccine, there is a need to strictly

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adhere to the set upper age limits, the first dose of either RV1or RV5 be administered between the ages of 6 wk and 14 wk6 d, and that the maximum age for administering the last doseof either vaccine should be 32 wk [6].

Cold Chain

Maintenance of the cold chain is a vital component inensuring that an effective vaccine is administered. All vac-cines should be kept at 2–8° centigrade temperature in therefrigerator. During a vaccination session, the vaccine to beadministered should be kept in the cold ice pack. Domesticrefrigerators are the most common choice for vaccinestorage in general practice, and are generally of three types:frost free, cyclic defrost, and bar refrigerators. Temperaturecontrol may be uneven in different areas of such refrigerators.In contrast, purpose built vaccine refrigerators feature a stable,uniform, and controlled cabinet temperature unaffected byambient heat. Their defrost cycle allows defrosting withoutrising in cabinet temperature.

Vaccine vial monitors (VVM) provide a continuouscheck on maintenance of cold chain preservation, but arelimited in that they can’t capture all micro climate

temperature variations that can deactivate immunisationproduct and exposure to freezing which contribute to thedegradation of freeze-sensitive vaccines.

BCG and measles vaccines are heat and light sensitiveand OPV is heat sensitive. DPT, DT, TT, Hepatitis B andphenolized Typhoid vaccines should not be frozen.

Adverse Reactions to Vaccines

Minor ReactionsSystemic Reactions—Fever, irritability, malaise, head-ache and non specific symptoms.Local Reactions—Redness, pain, limitation of move-ment, swelling, sterile abscess.

Moderate ReactionsHigh fever, seizure, unconsolable crying episode, hy-

potonic hyporesponsive episode, adenitis.Severe Reactions

Anaphylaxis, toxic shock syndrome, encephalopathy,GBSyndrome, myelopathy, sciatic and brachial neuritis,vaccine associated paralyitic poliomyelitis (VAPP), dis-seminated BCG infection, transmission of diseases.

Management of Anaphylaxis

& Immediate administration of epinephrine 1:1000 solu-tion 0.1 mg/kg IM (1 mg =1 ml) with maximum dose of0.3 mg in children and 0.5 mg for adult. Repeat every20 min × 3 doses if no improvement.

& Diphenhydramine 1 mg/kg IM/Orally, max 30 mg inchildren and 100 mg for adult.

& Cardio pulmonary resuscitation (CPR) if required.& Inform MO in charge/district immunization officer.

Vaccination in Adolescents (Table 4)

Adolescents are most neglected age group and the Nationalschedule mentions only administration of Tetanus toxoid at

Table 4 IAP recommendations for adolescent immunization

Vaccines Dose and schedule

TT/Td/Tdap Booster at 10, 16 y can be given inpregnancy in place of TT

Rubella As part of MMR or monovalent vaccineto girls at 12–13 y of age

MMR One dose at 12–13 y if not given earlier

Hepatitis-B Three dose at 0, 1 and 6 mo if notgiven earlier

Typhoid Vi polysaccharide vaccine every 3 y

Varicella Two doses at 1 mo interval

Hepatitis-A Two doses at 0 and 6 mo

HPV Three doses starting from 10 y onwardsat 0, 2, 6 or 0, 1, 6 mo

Table 5 Recommended immu-nization for travelers to devel-oping countries (ACIP)

Vaccines Length of travel(Brief<2 wk)

Length of travel(2wk-3 mo)

Length of travel(>3 mo)

Review age appropriate childhoodimmunization schedule

+ + +

Yellow fever for African countries + + +

Hepatitis-A + + +

Typhoid fever ± + +

Meningococcal disease ± ± ±

rabies ± + +

JE ± ± +

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10 and 16 y of age. However there are many diseases whichcan be prevented by age appropriate vaccination in adoles-cents. American Academy of Pediatrics has developed clear-cut guidelines for immunization in adolescents and evenIndian Academy of Pediatrics has given guidelines forpediatricians across the country to follow the recommenda-tions of IAP.

Vaccination for Travelers

Following Table 5 is a rough guideline for travelerscoming to developing countries. Some of the vaccinesare mandatory requirement for travelers. E.g., yellowfever vaccine for African nations and quadrivalent Me-ningococcal and OPV vaccine for Hajj pilgrims. Rabies,JE and Typhoid vaccines are recommended in countrieswith high endemicity of these diseases. For travelersand students going from India to developed countries,all age appropriate vaccines as per National scheduleshould be taken. Some American universities recom-mend Meningococcal vaccine and Tuberculin test to beadministered before joining the course but are notmandatory.

Summary

All age appropriate vaccines should be administered as perthe National immunization schedule of the country. Thecoverage of the vaccines should be improved which is stilllow in India. Proper precautions should be taken whileadministering any vaccine and the individuals should beobserved for 15 min after vaccination for any immediateserious adverse reactions. Resuscitation equipments includ-ing life saving drugs should be always kept in the immuni-zation room. All adverse reactions following immunizationshould be reported to the health authority. Immediate

treatment for anaphylaxis should be started if any such eventoccurs which can be life saving.

References

1. World Health Organization. Global immunization data. Geneva:WHO; 2011. available at http://www.who.int/immunization.

2. World Health Organization and United Nations Childrens Fund.Global immunization vision and strategy, 2006–2015. Geneva,Switzerland: WHO and UNICEF; 2005. (WHO/IVB/0505); avail-able at http://www.who.int/vaccine

3. Pickering LK, Baker CJ, Kimberlin DW, Long SS. 2009 Report ofthe Committee on Infectious Diseases, American Academy ofPediatrics. 28th ed. Daryaganj, New Delhi: Jaypee BrothersMedical Publishers PVT. Ltd; 2010. pp. 19–34.

4. Immunization Schedule of India; Govt of India, Ministry of Healthand Family Welfare, Nirman Bhawan, National vaccination policybook, MOHFW, Nirman Bhawan, New Delhi 2012. available athttp://www.mohfw.nic.in

5. Indian Academy of Pediatrics Committee on Immunization(IAPCOI). Consensus recommendations on immunization, 2008.Indian Pediatr. 2008;45:635–48.

6. Plotkin SA, Vidfor E. Polivirus Vaccine-Inactivated. In: PlotkinSA, Orenstein W, Offit P, eds. Vaccines. 5th ed. China: Elsevier;2007. pp. 605–29.

7. Sulter RW, Suleiman AJ, Malnkar PG, et al. Sequential use ofinactivated poliovirus vaccine in Oman. J Infect Dis. 1997;175:S15:235–40.

8. Singh J, Ravi RN, Dutta AK, et al. Immunogenicity of enhancedpotency inactivated polio vaccine. Indian Pediatr. 1992;29:1353–56.

9. Edwards KM, Decker MD. Pertussis Vaccine. In: Plotkin SA,Orenstein W, Offit P, eds. Vaccines. 5th ed. China: Elsevier;2007. pp. 399–434.

10. Black S, Eskola J, Whitney C, Shinfield H. Pneumococcal conju-gate vaccine and Pneumococcal protein vaccine. In: Plotkin SA,Orenstein W, Offit P, eds. Vaccines. 5th ed. China: Elsevier; 2007.pp. 531–68.

11. Granoff DM, Harrison LH, Borrow R. Meningococcal vaccines.In: Plotkin SA, Orenstein W, Offit P, eds. Vaccines. 5th ed. China:Elsevier; 2007. pp. 399–434.

12. Fredclark H, Offit PA, Parashar UD, Ward RL. Rota virus vaccine.In: Plotkin SA, Orenstein W, Offit P, eds. Vaccines. 5th ed. China:Elsevier; 2007. pp. 715–36.

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