Immunization is the process whereby a person is made immune or resistant to an infectious disease, typically by the administration of a vaccine. Vaccines stimulate the body’s own immune system to protect the person against subsequent infection or disease.

Babies are born with natural immunity against some diseases, which they get from their mothers (in utero) and by breastfeeding in the early days of their life. But as they grow, this immunity gradually decreases. Immunization further enhances their immunity and protects them against vaccine-preventable diseases.

Vaccines contain either weakened or killed versions of viruses or bacteria, or an antigenic substance prepared from the causative agent, or a synthetic substitute. Once administered in the body by injection, mouth or by aerosol, stimulate the immune response to produce “antibodies” targeting those infectious agents, thereby producing protection against infections. Each vaccine provides immunity against a particular disease; therefore, a number of vaccines are administered to children and pregnant women to protect them from many vaccine-preventable diseases.

The duration of immunity varies with different diseases and different vaccines. Life- long immunity is not always provided by either natural infection or vaccination. The protection provided by vaccines decreases gradually over time. Therefore, booster doses are sometimes recommended for certain vaccines, at specific age groups.

Immunization process starts when a child is in utero. Immunity developed from TT vaccine given to pregnant women passes to her child and protects from neonatal tetanus. Immunity against some infections, like measles, is transferred to child as passive immunity and protects from infection for some period after birth. Under National Immunization Schedule, BCG, OPV, and Hep B vaccines are given to child immediately after birth.

Age of administration of vaccines is decided by medical and public health experts after careful study of disease epidemiology and protective efficacy of different vaccines. Vaccines ensure best protection when they are given at the right time. India’s National Immunization Schedule has been designed to protect children since birth, and at the ages when they are vulnerable to specific vaccine-preventable diseases. The recommended age for vaccination by different vaccines aims to achieve the best immune protection to cover the period in life when vulnerability to disease is highest. When children are not vaccinated at all or get vaccinated beyond the recommended age, they remain unprotected and may get infected from a vaccine-preventable disease.

Government’s immunization programme serves to a wider community, while private providers serve only to families that approach to them for services. Universal Immunization Programme (UIP) implemented by Ministry of Health & Family Welfare (MoHFW), Government of India includes vaccines recommended by WHO and National Technical Advisory Group on Immunization (NTAGI). Its objective is to control transmission of diseases having public health significance that can lead to high mortality and morbidity among the community.

Private providers, on the other hand, follow immunization schedule recommended by Indian Academy of Paediatrics (IAP). It includes some vaccines that are not of public health significance and do not pose threat to a larger community. Therefore, vaccines provided in government’s programme are fewer as compared to those provided by private providers.

Both government and private sectors have same regulatory mechanisms and all vaccines are procured from government approved manufacturers. All vaccines are approved by Central Drugs and Standards Control Organization (CDSCO) which is the National Regulatory Authority (NRA). Drug Controller General of India (DCGI) heads the CDSCO and grants permission to conduct clinical trials; registers and controls the quality of vaccines.4

Use of vaccines in India’s Universal Immunization Programme (UIP) has resulted in successful eradication/elimination of three diseases from the country. These are smallpox (1977), poliomyelitis (2014) and maternal and neonatal tetanus (2015).

Yes. It is true that individual vaccination against a disease-causing pathogen can protect even those individuals in a community who have not been vaccinated against that disease or pathogen. A population with a high number of members with immunity to a particular disease or pathogen may give protection from that infection to the small number of its non-immune members. This phenomenon is known as “herd immunity” or “community immunity” or “population immunity”. This is only achieved when a very high proportion of community members are vaccinated, so it is difficult for the disease-causing organism to spread to unprotected persons because there are few of those people left.

It is only true for diseases where there is a person to person transmission. Herd immunity makes it difficult for disease-causing organism to spread through cycle of infection, multiplication and circulation among the vulnerable population.

Vaccines have been used for decades and have proven to be effective. Like any other medicine, no vaccine is 100% efficacious. The immunity produced by vaccines varies from child to child. There may be children who do not develop sufficient protective immunity against a disease-causing pathogen due to malnutrition, repeated episodes of diarrhoea leading to diminished immunity or individual specific immune response to a vaccine.

Because of these reasons, some children suffer from vaccine-preventable disease despite receiving vaccination against it. However, in such cases the disease is of less severity than in children who have never been vaccinated.

Vaccine hesitancy is the behaviour of parents, caregivers, or the community, who hesitate to get their children vaccinated in spite of immunization services being available and accessible. Inadequate immunization services due to non-availability of vaccines, absenteeism of vaccinators and long distances to vaccination centres contribute to this hesitancy. Other reasons for vaccine hesitancy are low perception of the benefits of vaccines, loss of wages, social beliefs, fear of AEFIs, inadequate IPC skills of health workers, geographical barriers.

Vaccine confidence is when parents, caregivers or the community understand the value of vaccination and voluntarily demand vaccination services as a right, whether these vaccinations are part of the RI schedule for their children or part of adult vaccinations such as TT for pregnant women. Vaccine confidence comes from adequate awareness about the benefits of vaccines, both to the individual and to the community, and the trust in the immunization service delivery system to be able to provide quality vaccination.

Vaccines are introduced in National Immunization Schedule for diseases that lead to high mortality and morbidity among children. Certain vaccines are introduced in selected states due to the following reasons;

• Whenever new vaccines are introduced in UIP, then initially, they are rolled out in some states (phased-wise introduction) and gradually expanded across all states and districts of the country. For example, Rotavirus Vaccine and PCV.
• Diseases, like Japanese Encephalitis, are endemic in certain districts and states only (i.e. restricted to a certain place due to environmental conditions). For such diseases, vaccines are introduced only in those areas which are affected by them.
• There are initiatives by the state government to introduce additional vaccines in their routine immunization, which are not part of National Immunization Schedule.

National Immunization Schedule is a vaccination plan that all children and pregnant women should follow and complete to ensure protection against vaccine-preventable diseases.

This schedule includes name of vaccine; recommended age/s of administration; total doses required; route and site of administration; and volumes of doses.

Under India’s Universal Immunization Programme 12 different vaccines are provided to beneficiaries free of cost, through government health system. These are – BCG, OPV, Hepatitis B, Pentavalent, Rotavirus, PCV, IPV, Measles/MR, JE, DPT, and TT. Out of these, Rotavirus Vaccine, PCV and MR are being introduced in a phased-wise manner across different states. JE vaccine is given only in the districts where Japanese Encephalitis is endemic. Vaccines administered in UIP and the diseases prevented by them are as follows

BCG OPV: Hepatitis B

Penta: Diphtheria (Gal Ghotu), Pertussis (Whooping Cough, Kaali Khansi/ Kukkar Khansi), Tetanus, (Dhanustambh), Hib infection (causing pneumonia and meningitis), and Hepatitis B

Rotavirus Vaccine: IPV, Measles, MR*, Rotavirus diarrhoea, Poliomyelitis, Measles (Khasra or Govar), Measles and Rubella

JE*: Japanese Encephalitis or Acute Encephalitis Syndrome (AES)

or Brain Fever (Dimagi Bukhar)

DPT: Diphtheria, Pertussis, and Tetanus

TT:  Tetanus (in new-born and pregnant women)

PCV*: Pneumococcal Pneumonia

A fully immunized child is one who has received all vaccines recommended in the National Immunization Schedule in required doses, before completing one year of age.

For the purpose of monitoring and evaluating the programme, a child below 1 year of age who has received one dose of BCG, Measles/MR along with 3 doses of OPV, Pentavalent Vaccine and two doses of IPV is said to be fully immunized. However, for the purpose of the programme and to ensure that the child is completely protected, all other vaccines applicable to a child below one year of age should be provided as per the immunization schedule, like PCV (3 doses), RVV (3 doses), JE (1 dose), wherever applicable.

A child who has received all vaccines recommended for the first and second year in the National Immunization Schedule is said to be completely immunized.

• First year: One dose of BCG, Measles/MR* and JE vaccines*, 3 doses of OPV, Pentavalent vaccine, Rotavirus vaccine* and PCV*, and 2 doses of IPV
• Second year: Second dose of Measles/ MR* and JE vaccines*, and one booster dose of OPV and DPT

From a service delivery perspective:

• Left outs are those children who have never been vaccinated or reached (thus

remaining unimmunized);

• Drop outs are those children who started vaccination but did not complete the schedule (thus remaining partially immunized).

From behavioural perspective, a large percentage of dropouts is a serious problem because it reflects the poor perception of the parents/caregivers about the benefits of vaccination or of the immunization service delivery system, or both, combined with other barriers that forces them to place immunization on a low priority.6

Vaccines introduced in Universal Immunization Programme during last few years are JE (2006), Hepatitis B (2007), Pentavalent (2011), IPV (2015) and Rotavirus Vaccine (2016). Pneumococcal Conjugate Vaccine (PCV) and Measles-Rubella (MR) are the latest additions rolled out under UIP (2017).

No. There is no need to restart the series or schedule again in case a child has received some doses of scheduled vaccines but is brought late for the subsequent doses. If the child is brought late, you should give the next dose of the vaccine and motivate the parents to bring the child for the remaining doses at the recommended interval as per the immunization schedule.

According to National Immunization Schedule some vaccines have an upper age limit for administration and these vaccines should not be administered once that age limit is crossed.

The vaccines should be given till the following ages as per UIP guidelines:

• BCG: up to one year of age
• OPV: up to five years (OPV zero dose till 15 days of birth)
• Measles/MR: up to five years (in MR campaigns, vaccine is given to 9 months to 15 years age group)
• DPT: up to 7 years
• JE: up to 15 years

Only the above-mentioned vaccines have upper age limits. Efforts should be made to ensure that all vaccines are given at the recommended ages, or closer to it. For pentavalent, IPV, PCV and Rotavirus vaccines, if at least one dose is given before one year of age, then remaining doses can be administered and schedule must be completed irrespective of the age of child. If the first dose is not administered before one year of age, then these vaccines cannot be administered to the child under UIP.

Age of administration for different vaccines has been recommended in National Immunization Schedule taking into consideration maximum benefit in terms of immunity generation, reduction in disease incidence, and mortality and morbidity. The schedule has been designed to ensure protection against vaccine preventable diseases to children at ages when they are most vulnerable. After attaining a certain age, children acquire natural immunity to some infections (like childhood tuberculosis), or cross vulnerable age period when a vaccine- preventable disease can be life threatening.

Immunity or protective effect generated by some vaccines gradually diminishes over time and increases vulnerability to target infections. For such vaccines, booster doses are administered after receiving initial doses as it boosts immunity and enhances protection level against specific vaccine-preventable disease. For example: DPT, OPV and PCV.

Yes. Most vaccine-preventable diseases (for example, Diphtheria, Tetanus, Rotavirus diarrhoea, Hib pneumonia and JE) after an episode of full-blown infection and disease do not confer long-term immunity. Therefore, in these cases a child will still require all recommended doses of the vaccine as per the national immunization schedule.

Some vaccine-preventable diseases are caused by different strains of same pathogenic organism. In these cases, infection by one strain does not confer immunity against other strains and will require vaccination to ensure full protection. Example: Bivalent OPV as currently given in UIP provides protection against poliovirus types 1 and 3. Therefore, administration of this vaccine will still be required for a child who got infected by the type 1 poliovirus in past, as s/he is vulnerable for infection from type 3 poliovirus.