Routine Immunization
A cornerstone of the polio eradication strategy is the need to ensure high (more than 80%) immunization coverage of children in the first year of life, with at least three doses of oral polio vaccine as part of national routine immunization schedules.
While routine immunization alone cannot eradicate the disease, good routine oral polio vaccine coverage increases population immunity, reduces the incidence of polio and makes eradication feasible.
If uniformly high immunization coverage is not maintained, pockets of non-immunized children build up, favouring continued spread and outbreaks of the poliovirus.
According to WHO/UNICEF immunization coverage estimates, 86% of infants received three doses of oral polio vaccine in 2010, compared with 75% in 1990.
Polio-free countries must continue to ensure high levels of immunization coverage to prevent the re-establishment of poliovirus through importations from other countries. This can happen through international travellers, migrant populations or population sub-groups who refuse immunization.
An increasing number of industrialized, polio-free countries are using inactivated polio vaccine (IPV) in routine immunization schedules. IPV is not recommended for routine use in polio-endemic countries or in developing countries at risk of poliovirus importations as it does not stop transmission of the virus, and is more complex to administer and costly than oral polio vaccine.
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Supplementary Immunization
Mass immunization campaigns, known as National Immunization Days (NIDs) or supplementary immunization activities (SIAs), are one of the four pillars of eradication. This supplementary immunization is intended to complement – not replace – routine immunization.
The aim of mass campaigns is to interrupt circulation of poliovirus by immunizing every child under five years of age with two doses of oral polio vaccine, regardless of previous immunization status.
The idea is to catch children who are either not immunized, or only partially protected, and to boost immunity in those who have been immunized. This way, every child in the most susceptible age group is protected against polio at the same time – instantly depriving the virus of the fertile seedbed on which its survival depends.
National Immunization Days (NIDs)
National Immunization Days are conducted in two rounds, one month apart. Because oral polio vaccine does not require a needle and syringe, volunteers with minimal training can serve as vaccinators, increasing the number of vaccinators well beyond the existing trained health staff.
Three to five years of NIDs are usually required to eradicate polio, but some countries require more time, especially those where routine immunization coverage is low. NIDs are normally conducted during the cool, dry season because logistics are simplified, immunological response to oral polio vaccine is improved and the potential damage to heat-sensitive vaccine is reduced.
Synchronized NIDs
Increasingly, neighbouring countries are coordinating, or “synchronizing” their National Immunization Days. This ensures that children crossing borders for any reason are identified and immunized. It also allows health teams to cross borders and immunize children in pockets of territory otherwise isolated by rivers or mountains, or on islands that may be less accessible from the other side.
This approach was first used between countries of eastern Europe and central Asia, in a successful campaign called “Operation MECACAR.”
Massive synchronized campaigns among west and central African countries have taken place repeatedly following importations of poliovirus: in March 2010, 85 million children were vaccinated in 19 countries. Political, religious and traditional leaders teamed up to launch the activities, and tens of thousands of vaccinators went house-to-house over three days to administer the vaccine directly to every child.
Similar synchronized efforts have been undertaken along the borders of Afghanistan and Pakistan.