What is Polio?
To the average American living in 2020, the word “polio” conjures an image of a crippling disease that only existed well in the past. However, this is far from the truth. While it has not been prevalent in the Untied States for some time now, polio, caused by the poliovirus, is still a major global health threat, not only to countries with endemic polio, but also countries like the United States which have been polio-free for decades. The full name for polio is poliovirus, and it is a disease which can result in paralysis and death. Broadly, there are two kinds of poliovirus: wild poliovirus (WPV) and vaccine-derived polio virus (VDPV). According to an article posted by the International Association for Medical Assistance to Travelers (IAMAT), there are three types of wild-type poliovirus (types 1, 2, and 3); types 2 and 3 are thought to have been completely eradicated, yet WPV1 (wild poliovirus type 1) is still seen in outbreaks around the world and is even endemic in countries such as Pakistan and Afghanistan.
Polio: The Past 6 Months
In the past six month, we have seen an increase in the number of polio outbreaks around the world. According to the previously mentioned IAMAT article, in 2019 168 WPV1 cases were reported, all of which occurred in either Pakistan or Afghanistan. However, according to the same source, the number of vaccine-derived poliovirus outbreaks has increased recently. IAMAT reports that these outbreaks occurred in 16 countries located in the regions of Africa, the Eastern Mediterranean, Southeast Asia, and the Western Pacific. It also reports that an outbreak occurred in the Philippines, a country that had not reported a polio case for 19 years prior to 2019. While the United States has been polio-free since 1979 according to a CDC post, it only takes one traveler from a country experiencing polio to reintroduce the virus to an increasingly unvaccinated American population.
IVP and OPV
IVP and OPV are the shorthand terms for the two widely used polio vaccines. They stand for inactivated polio vaccine and oral polio vaccine, respectively. According to our textbook, the IPV or Salk vaccine was developed in the mid-1950s and is a subunit vaccine consisting of key poliovirus particles. While this vaccine effectively invokes an immune response, it requires multiple doses which both increases cost of administration and decreases patient adherence. The OPV or Sabin vaccine came about in 1961. The OPV is an attenuated form of the poliovirus. This means that it is a non-virulent virus that is still capable of replicating inside a susceptible host. For this reason, the OPV requires only one oral dose, as the attenuated virus is able to replicated and thus induce a more sustained and powerful immune response. However, because the attenuated strain in the OPV is actively replicating, it does have the possibility of mutating. Sometimes, a mutation can cause the virus to become virulent, causing disease in the recipient. For this reason, the United States has discontinued use of the OPV in light of the fact that the country has been polio free for a long time. However, I think if polio were reintroduced into the United States, we would return to an IPV and OPV dosing schedule.
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