Polio vaccine

Polio vaccines are vaccines used to prevent poliomyelitis (polio). Two types are used: an inactivated poliovirus given by injection (IPV) and a weakened poliovirus given by mouth (OPV). The World Health Organization recommends all children be fully vaccinated against polio. The two vaccines have eliminated polio from most of the world, and reduced the number of cases reported each year from an estimated 350,000 in 1988 to 33 in 2018. The inactivated polio vaccines are very safe. Mild redness or pain may occur at the site of injection. Oral polio vaccines cause about three cases of vaccine-associated paralytic poliomyelitis per million doses given. This compares with 5,000 cases per million who are paralysed following a polio infection. Both are generally safe to give during pregnancy and in those who have HIV/AIDS but are otherwise well. The first polio vaccine was the inactivated polio vaccine. It was developed by Jonas Salk and came into use in 1955. The oral polio vaccine was developed by Albert Sabin and came into commercial use in 1961. They are on the World Health Organization's List of Essential Medicines, the most effective and safe medicines needed in a health system. The wholesale cost in the developing world is about US$0.25 per dose for the oral form as of 2014. In the United States, it costs between $25 and $50 for the inactivated form. Interruption of person-to-person transmission of the virus by vaccination is important in the global polio eradication, since no long-term carrier state exists for poliovirus in individuals with normal immune function, polio viruses have no nonprimate reservoir in nature, and survival of the virus in the environment for an extended period of time appears to be remote. When the current formulation of IPV is used, 90% or more of individuals develop protective antibodies to all three serotypes of polio virus after two doses of inactivated polio vaccine (IPV), and at least 99% are immune to polio virus following three doses. The duration of immunity induced by IPV is not known with certainty, although a complete series is thought to provide protection for many years. Oral polio vaccines proved to be superior in administration, eliminating the need for sterile syringes and making the vaccine more suitable for mass vaccination campaigns. OPV also provided longer-lasting immunity than the Salk vaccine, as it provides both humoral immunity and cell-mediated immunity. One dose of OPV produces immunity to all three poliovirus serotypes in roughly 50% of recipients. Three doses of live-attenuated OPV produce protective antibodies to all three poliovirus types in more than 95% of recipients. OPV produces excellent immunity in the intestine, the primary site of wild poliovirus entry, which helps prevent infection with wild virus in areas where the virus is endemic. The live virus used in the vaccine can rarely shed in the stool and can rarely spread to others within a community. The live virus also has stringent requirements for transport and storage, which are a problem in some hot or remote areas. As with other live-virus vaccines, immunity initiated by OPV is probably lifelong. The trivalent (against wild types 1, 2, and 3) OPV has been used to nearly eradicate polio infection worldwide. Led by The Global Polio Eradication Initiative, 155 countries switched to use the bivalent (against wild type 1 and 3) between 17 April and 1 May 2016. The bivalent OPV is at more effective against type 1 and 3 but does not cover type 2. The United States as of 2017 continues to recommend the use of a trivalent version, but a fully inactivated version.