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Emergent Preparatory Group

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Onadezhda Udavis
Onadezhda Udavis

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The inactivated polio vaccine (IPV, or Salk) contains trivalent fully inactivated virus, administered by injection. This vaccine cannot induce VAPP nor do cVDPV strains arise from it, but it likewise cannot induce contact immunity and thus must be administered to every individual. Added to this are greater logistical challenges. Though a single dose is sufficient for protection, administration requires medically trained vaccinators armed with single-use needles and syringes. Taken together, these factors result in substantially higher delivery costs.[22] Original protocols involved intramuscular injection in the arm or leg, but recently subcutaneous injection using a lower dose (so-called fractional-dose IPV, fIPV) has been found to be effective, lowering costs and also allowing for more convenient and cost-effective delivery systems.[23][24] The use of IPV results in serum immunity, but no intestinal immunity arises. As a consequence, vaccinated individuals are protected from contracting polio, but their intestinal mucosa may still be infected and serve as a reservoir for the excretion of live virus. For this reason, IPV is ineffective at halting ongoing outbreaks of WPV or cVDPV, but it has become the vaccine of choice for industrialized, polio-free countries.[22]


While vaccination has played an instrumental role in the reduction of polio cases worldwide, the use of attenuated virus in the oral vaccine carries with it an inherent risk. The oral vaccine is a powerful tool in fighting polio in part because of its person-to-person transmission and resulting contact immunity. However, under conditions of long-term circulation in undervaccinated populations, the virus can accumulate mutations that reverse the attenuation and result in vaccine virus strains that themselves cause polio. As a result of such circulating vaccine-derived poliovirus (cVDPV) strains, polio outbreaks have periodically recurred in regions that have long been free of the wild virus, but where vaccination rates have fallen. Oral vaccines can also give rise to persistent infection in immunodeficient individuals, with the virus eventually mutating into a more virulent immunodeficiency-associated vaccine-derived poliovirus (iVDPV). In particular, the type 2 strain seems prone to reversions, so in 2016 the eradication effort abandoned the trivalent oral vaccine containing attenuated strains of all three virus types and replaced it with a bivalent oral vaccine lacking the type 2 virus, while a separate monovalent type 2 vaccine (mOPV2) was to be used only to target existing cVDPV2 outbreaks. Further, a novel oral vaccine targeting type 2 (nOPV2) that has been genetically stabilized to make it less prone to give rise to circulating vaccine-derived strains is now in limited use.[32][21] Eradication efforts will eventually require all oral vaccination to be discontinued in favor of the use of injectable vaccines. These vaccines are more expensive and more difficult to deliver, and they lack the ability to induce contact immunity because they contain only killed virus, but they likewise are incapable of giving rise to vaccine-derived viral strains.[33][34]


In 1995, Operation MECACAR (Mediterranean, Caucasus, Central Asian Republics, and Russia) was launched; National Immunization Days were coordinated in 19 European and Mediterranean countries.[83] In 1998, Melik Minas of Turkey became the last case of polio reported in Europe.[84] In 1997, Mum Chanty of Cambodia became the last person to contract polio in the Indo-West Pacific region.[85] In 2000, the Western Pacific Region (including China) was certified polio-free.[85]


By 2001, 575 million children (almost one-tenth the world's population) had received some two billion doses of oral polio vaccine.[87] The World Health Organization announced that Europe was polio-free on 21 June 2002, in the Copenhagen Glyptotek.[88]


In August 2003, rumors spread in some states in Nigeria, especially Kano, that the vaccine cau




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