The vaccine most used globally

is the trivalent oral polio vaccine (tOPV or ‘Sabin vaccine’), which is effective against all three types of wild poliovirus. Use of tOPV can result in the ‘passive’ immunization of people living in areas of poor hygiene and sanitation who have not been directly vaccinated, as the virus continues to be excreted through the feces into the environment for several weeks after vaccination. A further advantage to its use is its cost, estimated to be between 11 and 14 US cents per dose [7]. There are also two more oral polio vaccines in use today: the monovalent vaccine (mOPV) and the bivalent vaccine (bOPV). In children being immunized for the first time, the monovalent vaccine (mOPV), consisting of just one type of the live

attenuated strains of poliovirus, provides a greater immunity to the specific type of poliovirus being targeted and also provides increased immunity for the same number of Tucidinostat chemical structure doses compared with tOPV. This may be because there is no competition from the other two virus types in the vaccine [8]. The bivalent vaccine (bOPV) consists of live attenuated strains of both type-1 and type-3 poliovirus and improves the efficiency and impact of vaccination campaigns in areas where both types of poliovirus co-circulate. It is more effective than tOPV and Selonsertib chemical structure almost as effective as mOPV in achieving protection [9]. Unfortunately, in very rare cases, (approximately 1 in every 2.7 million first doses of the vaccine), the oral polio vaccines can cause a find more condition known as vaccine-associated paralytic polio [7]. Even more concerning is the potential for the live attenuated strains of the vaccine viruses to revert and re-acquire neurovirulence, resulting in circulating vaccine-derived polioviruses (cVDPVs) [10]. cVDPVs could pose a threat in a post-eradication world, with the ability to cause devastating outbreaks

of polio at a time when immunity levels are reduced. In HAS1 most high-income countries, where the risk of polio infection is low, the inactivated polio vaccine (IPV or ‘Salk vaccine’) is used. IPV consists of “killed” strains of all three polioviruses, which is delivered via an injection. As it is not a “live” vaccine, IPV poses no risk to the recipient of vaccine-associated paralytic polio, nor is there any possibility of cVDPVs emerging [11]. However, it does need to be administered by a trained health worker, induces very low levels of immunity in the intestine and is over five times more expensive than the oral polio vaccine [11]. Following its launch in 1988, the GPEI had a promising start and the Americas was the first WHO Region to be certified polio-free of all three types of wild poliovirus in 1994. By the year 2000, the global incidence of polio had been reduced by over 99% [12] and every endemic country had implemented some form of polio-eradication strategy.