Updated 02.12.2019

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Background

Poliovirus and Poliomyelitis

The disease caused by the poliovirus is called poliomyelitis or “infantile paralysis” but is also often just referred to as polio. 

Poliovirus can only infect humans and has been circulating for many thousands of years. It is generally believed that the infections became more severe in the first decades of the 20th century as children became infected later in life. Before that, children became infected at a younger age, when they still had some protective antibodies derived from their mother that could milden or prevent the development of severe polio infection. The name “infantile paralysis” stems from poliovirus being so contagious that infection often happens at an early age. However, adults are just as susceptible for an infection as children are and suffer the same disease progression. 

The poliovirus is highly contagious and transmission occurs via the fecal-oral route, but contact transmission (oral-oral) is also possible. The virus is primarily an enteric virus that replicates in the gut mucosa with no or mild symptoms. Entry into the central nervous system is not essential for poliovirus replication, but it can have devastating consequences for the host.

Approximately one out of 200 persons infected with poliovirus develops poliomyelitis with irreversible paralysis. Of these, 5-10% die as paralysis spreads to the breathing apparatus. People who recover from transient paralysis caused by poliovirus infection, can later in life develop post-polio syndrome, which is characterised by progressive muscle pain and weakness and generalized fatigue.

There are three serotypes of wild-type polioviruses (WPV1, WPV2 and WPV3), all of which can give rise to poliomyelitis. WPV2 and WPV3 have been eradicated.

Polio vaccines

There are two types of polio vaccines. The Oral Polio Vaccine (OPV) is administered as a few drops directly into the mouth, while the Inactivated Polio Vaccine (IPV) is given via injection. Between 1963 and 2005, both vaccines were commonly used in Denmark and many children received both types of vaccines. Both vaccines are safe and provide full protection against poliovirus.

OPV consists of live attenuated viruses (also referred to as Sabin strains) that initiate an infection in the gut. For a period of time, a vaccinated person will excrete attenuated poliovirus in their stool. OPV has been widely used in developing countries, as it is cheap to produce, easy to administer and provides full protection. Unfortunately, in communities with poor sanitation and where the population is under-vaccinated, the virus can start to circulate in the population, and over time revert to a virulent form that can cause poliomyelitis. As part of the WHO initiative to eradicate poliovirus (GPEI), the use of OPV will be phased out and replaced with IPV.

IPV is based on formalin-inactivated wild-type poliovirus, does not cause an active infection in the gut as OPV, and is often given in combination with other vaccines (e.g. diphtheria, tetanus and pertussis).

Vaccination coverage in Denmark (before and now)

Denmark was the second country in the world to start vaccinating children against polio (in 1955). Since 1959, the polio vaccine has been a part of the national child vaccination programme. The first polio vaccine used in Denmark was the IPV. In 1963 the IPV was supplemented with the use of OPV at the age of 2, 3 and 4 years of age. Starting in 2001, OPV was phased out in Denmark as part of GPEI.

The vaccination programme has been very successful and the last endemic case of poliomyelitis in Denmark was in 1976. In Denmark, IPV is still a part of the national programme for child vaccination and is given at the ages of 3, 5 and 12 months and at 5 years.

Poliovirus Potentially Infectious Materials (PIM)

Due to the use of OPV in Denmark up until 2004, there is a likelihood that PIM are stored in sample collections in Denmark.

Poliovirus is very stable and can remain infectious for a long time if it is stored in the right conditions. Viable, infectious polioviruses can therefore be present in certain types of clinical samples and materials, also those collected for other purposes than poliovirus diagnostics.

  • These materials are called PIM, and they include:
  • Human faecal or respiratory samples
  • Concentrated sewage
  • Clinical samples from humans with suspected poliovirus infection for diagnostic purposes
  • Extracted virus or nucleic acids, complementary DNA, cDNA (purified from faecal samples, respiratory samples or sewage) inoculated or transfected in poliovirus permissive cells
  • Full-length poliovirus genome.

Materials listed above are only PIM if both the following conditions are fulfilled:

  • They were collected when and where WPV was circulating, or when OPV was in use. In Denmark, the last endemic case of polio was registered in 1983, and OPV was in use until 2004. For samples originating from other countries, please refer to the PIM-Annex 2.
  • They were kept under conditions that permit poliovirus survival (poliovirus can survive in clinical and environmental samples indefinitely at -20℃, for months in a refrigerator, and for hours at room temperature.

Facilities or research institutions are required to identify whether they are in possession of PIM. If you suspect that your facility has PIM, you must contact CBB.

 

 

Contact us

Centre for Biosecurity and Biopreparedness 
Statens Serum Institut

5 Artillerivej
DK-2300 Copenhagen S

Telefon: +45 32688127
Email: cbb@ssi.dk