What is Poliomyelitis?

What is Poliomyelitis?

What is Poliomyelitis?

Poliomyelitis is a viral disease caused by the poliovirus, which, in rare cases, can affect the nervous system and lead to paralysis or death. The name "polio" comes from the Greek words "polio" (grey) and "myelin" (marrow), reflecting its impact on the spinal cord[1].

Poliovirus comes in three variants: type 1, type 2 and type 3. Essential to note is that acquired immunity against one type does not protect against the other two. This virus is an enterovirus that exclusively infects humans and primarily inhabits the gastrointestinal tract[2].

Most polio infections, approximately 95%, are asymptomatic. Of those who develop symptoms, 4-8% show mild signs, including flu-like illnesses, respiratory and gastrointestinal problems. About 1% of those infected develop a form of aseptic meningitis, with symptoms that include severe spasms and typically resolve within 10 days.[3]

Paralytic polio, the most severe manifestation of the disease, affects less than 1% of people exposed to the virus. This condition can arise between 1 to 18 days after the initial infection and the symptoms of paralysis tend to worsen over the course of 2 to 3 days. An asymptomatic period of 7-10 days can be observed between the first signs and the most severe symptoms[4].

Recently, there has been an increase in cases of paralytic poliomyelitis associated with vaccine-derived poliovirus (VDPV) because OPV (Oral Polio Vaccine), a live attenuated virus vaccine, can replicate in the intestine and be excreted in the feces. Excreted vaccine virus has the potential to mutate genetically and cause paralytic poliomyelitis. VDPVs are classified into three categories:[-5 6]  

  • Circulating VDPV (cVDPV) – occurs in communities where individuals remain susceptible to wild-type polio or VDPV due to inadequately administered polio vaccination campaigns or lack of immunity to polio;
  • Immunodeficiency (iVDPV) - these strains are found in individuals with primary immunodeficiency (PID).
  • Ambiguous VDPV (aVDPV) - these are strains isolated from non-immunodeficient individuals or found in wastewater of which the source is unknown.

Wild-type polio type 2 was declared eradicated worldwide in 2015[7] and, similarly, on October 24, 2019, the Global Polio Eradication Initiative (GPEI) announced the global eradication of wild-type polio type 3.[8]

In September 2015, following the announcement of the eradication of wild-type polio globally, public health officials moved quickly to discontinue the use of trivalent OPV (vaccine containing vaccine strains of poliovirus types 2, 1 and 2) and replace it with a bivalent OPV containing only the vaccine strains of poliovirus types 3 and 1.[9] This initiative was implemented to stop the spread of VDPV type 2 (cVDPV2), which had caused multiple polio epidemics in several countries.[10] Since 2000, there have been 1.085 cases of paralytic polio associated with cVDPV, and the majority of cases – 932 (86%) – were caused by cVDPV2.[11]

Despite the elimination of type 2 polio from the OPV in spring 2016,[12] Cases of paralytic polio associated with cVDPV2 continued to occur. In 2019, cVDPV2 outbreaks were reported in the Philippines and several African countries.[13] This prompted health officials to reintroduce a type 2 OPV, and as of April 2016, approximately 300 million doses have been administered in regions where cVDPV2 outbreaks have occurred. Issues associated with the reintroduction of live OPV type 2 have included the risk that its use could potentially lead to additional cVDPV2 cases and outbreaks.[14]

Wild-type polio type 1 is the only strain of poliovirus currently circulating, and 2018 cases were detected globally in 33, including 12 in Pakistan and 21 in Afghanistan.[15] However, in 2018, 6.732 cases of VAPP associated with the use of Sabin OPV and 104 cases of VDPV paralysis were recorded. These cases were identified after testing was completed on stool samples from 190.055 people diagnosed with acute flaccid paralysis (AFP).[16]

IMPORTANT NOTE: Corvelva invites you to get in-depth information by reading all the sections and links, as well as the manufacturer's product leaflets and technical data sheets, and to speak with one or more trusted professionals before deciding to vaccinate yourself or your child. This information is for informational purposes only and is not intended as medical advice.

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