Why Pulse Polio?

Oral Polio Vaccine

The oral polio vaccine is a suspension of over 1 million particles of polioviruses type 1, 2 and 3 together. It is supplied with a stabilizing agent, namely magnesium chloride. Therefore the potency is quite stable under refrigeration or freezing. Several cycles of freezing and thawing do not reduce the potency. When OPV is given by mouth, the vaccine viruses go through the stomach and reach the intestines where they must establish infection ( = vaccine virus take) before an immune response may occur. The viruses survive the acidity of the stomach. However, for reasons not clearly understood, the ‘take’ rate is relatively low in our children.

For the above reason, multiple doses of OPV are necessary before 90 – 95% of children develop immune responses to all 3 poliovirus types. It is for this reason that the IAP recommends at least 4 routine doses of OPV, during infancy and 2 more repeat doses at 15 – 18 months and 5 years. In addition to the “Routine OPV doses”, “Pulse OPV doses every year on National Immunization days (NID’s) till the age of 5 years are also mandatory.

In order to ensure that vaccinated children do not participate in the chain of transmission of wild (pathogenic) polioviruses, a high level of gut immunity should be induced in them. For this reason also multiple doses of OPV are necessary.

Eradication is defined as no case of paralytic poliomyelitis by wild polio virus in last 3 calendar years along with absence of wild polio virus in the community, where excellent clinical and virological surveillance exists and the coverage of routine OPV is more than 80%.

Polio elimination is defined as Zero cases of paralytic poliomyelitis by the wild polio virus in one calendar year with other criteria same as in eradication.

• Adequate immunization is the method of eradication
• Clinical surveillance is the method to identify AFP status
• Virological investigations are necessary to document confirmation of polio virus.

In developing countries with high (pre-immunization era) incidence of polio, such as in India, 3 or 4 doses of OPV given to even 90% or more infants, did not result in polio eradication. In such countries with routine immunization of 4-6 doses of OPV and a near 100% coverage during annual pulse immunization - Pulse Polio Immunization, (PPI) will be necessary to achieve eradication. Surveillance must detect all cases of Acute Flaccid Paralysis (AFP), report them and investigate for poliovirus etiology. When any poliovirus is detected it should be examined by genomic analysis to identify it as wild poliovirus and to distinguish from vaccine strain of poliovirus, to facilitate recording the incidence of Vaccine Associated Paralytic Poliomyelitis (VAPP).

Why Pulse Polio?

On National Immunization Days (NID’s), pulse doses of oral polio vaccine has to be administered, as simultaneous feeding of the vaccine to all susceptible infants and children, would produce immunity to all and prevent wild poliovirus to multiply in the gut. Thus, wild polio virus cannot grow in susceptive host. Therefore, it is mandatory to administer all recommended doses in NID’s so that no wild poliovirus remains in the circulation.

Inject able Killed Polio Vaccine (IPV)

IPV is formaldehyde killed poliovirus grown in monkey kidney cell/human diploid cells containing 20, 8 & 32 D antigen against type 1, 2 and 3 poliovirus respectively. It is highly immunogenic. Seroconversion is 90-95%, after 2 doses and 99% after 3 doses. It produces excellent humoral immunity as well as local pharyngeal and possible intestinal immunity. The vaccine is very safe. However, it is not available at present in the Indian market for routine use and is licensed only for use in immunocompromised children.

Summary: Oral Polio Vaccine

• Live attenuated Poliovirus types 1, 2 and 3 developed by SABIN, 1961
• Temperature sensitive, store frozen or refrigerated
• Can be given simultaneously with any other vaccine
• Vaccine virus take = infection of GI tract
• Multiple doses necessary to ensure vaccine virus take and antibody response to all 3 types of polioviruses
• First dose is recommended in the newborn period or as early as possible
• IAP recommends additional doses of OPV as a part of Pulse Polio programme every year till the age of 5 years

Summary: Injectable (Killed) Oral Polio Vaccine

• Formaldehyde Killed Polio Virus grown in monkey kidney / human Diploid cell
• Contains 20, 8 and 32 D antigen units against type 1, 2 and 3 Polio Viruses respectively
• Seroconversion 90-95% after 2 doses and 99% after 3 doses
• Thermo stable and is indicated in Immunocompromised individuals, HIV infection and disease.

Dr Marwah