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The second part of the four-pronged strategy involves mass immunization campaigns, known as National Immunization Days (NIDs). 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 5 years of age with two doses of OPV, regardless of previous immunization status.
In 2003 for example, 415 million children under five years were immunized during National Immunization Days in 55 countries using over 2.2 billion doses of oral polio vaccine (OPV).
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.
NIDs are conducted in two rounds, one month apart. Because OPV does not require a needle and syringe, volunteers with minimal training can serve as vaccinators, increasing the number of vaccinators well beyond the existing staff of a country's Ministry of Health. For example, a recent NID in India deployed two million volunteers to immunize over 150 million children in just a few days.
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 OPV is improved and the potential damage to heat-sensitive OPV is reduced.
"SYNCHRONISED" NIDSAs the wild poliovirus doesn't distinguish between borders, neigbouring countries are increasingly coordinating, or "synchronising" their NIDs. This ensures children crossing borders for any reason are identified and immunized. Coordinated planning also allows health teams to cross borders themselves, to immunize children on an island which may be less accessible from the other side, or those in pockets of territory otherwise isolated by rivers, mountains or other impassable terrain.
On 23 February, 2004 10 countries across west and central Africa held simultaneous polio immunization campaigns, targeting 63 million children in Benin, Burkina Faso, Cameroon (20 February), Central African Republic, Chad (joined in March), Ghana, Niger, Nigeria, Ivory Coast and Togo. 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.
This approach was first used between countries of Eastern Europe and Central Asia, in a successful campaign called "Operation MECACAR." Another massive synchronised campaign amongst 17 west and central African countries in autumn 2000 dramatically reduced wild poliovirus transmission by immunizing 76 million children in the same week. In Angola, Congo, the Democratic Republic of the Congo and Gabon, 16 million children were immunized during three rounds of synchronised NIDs in 2001. Finally, similar synchronised efforts have been undertaken along the borders of Afghanistan and Pakistan, where the poliovirus freely circulates.
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