Poliomyelitis is a disease caused by the poliovirus. Most people infected with poliovirus have subclinical infections, meaning that they do not develop noticeable symptoms. This is an important factor to consider when discussing poliomyelitis because it allows for the disease to be spread more rapidly. However, people who do develop symptoms will usually have symptoms that resemble the flu. For example, symptoms might include sore throat, fever, tiredness, nausea, headache, and stomach pain. On rare occasions, people might develop symptoms that affect the brain and spinal cord, such as meningitis, paralysis, and paresthesia. Only people infected with the poliovirus that produces CNS-related symptoms are considered to have poliomyelitis. It is a very contagious disease and spreads through human to human contact. There are two types of vaccines available for polio, which include a live, attenuated vaccine and an inactivated one.
The live vaccine, created by Albert Sabin, is administered orally and is thus termed OPV, oral poliovirus vaccine. This form of poliovirus vaccine has not been administered in the US since 2000, due to a variety of reasons. The biggest and most concerning reason is that the mutated, safe form of the virus given to the patient can mutate in the intestine, where it replicates, and cause disease. In fact, in areas where the OPV is still in use, vaccine-derived poliovirus is sometimes more prevalent than wild-type poliovirus. The reason this form of the vaccine is still in use in these countries is because wild-type poliovirus remains an imminent threat for the people that inhabit those regions. While the inactivated form of the disease does provide similar immunity to the virus as the live form, it does not produce antibodies that can neutralize the viral particles before they infect the cell. This is important as it helps reduce the spread of the disease. People who only receive the inactivated form of the vaccine can still infect others, who are unvaccinated, through their feces or through other forms of direct contact. Another related reason why the OPV is no longer in use in the US is the decreased prevalence of wild-type poliovirus in the US. Health officials decided that the risks associated with the live type version of this vaccine did not outweigh its benefits of decreased risk of spread, which would prove to only be beneficial to countries where the vaccine is not as routinely given or the wild-type version still exists at an extensive level. The other form of the vaccine, which was briefly mentioned above, is the inactivated form of the vaccine, created by Jonas Salk, and termed IPV, inactivated poliovirus vaccine. The one downside to this vaccine is that it requires multiple doses to be the most effective at preventing poliovirus. According to the CDC, it requires three doses to provide 99% immunity. However, they suggest that four doses be given to children starting at two months of age to 6 years of age. This can be a problem if children need to travel to areas more affected by wild-type poliovirus. Although, there are much fewer risks associated with IPV, which is why it is now used in replacement of OPV in the US.
In an attempt to eliminate poliovirus in a global setting, an organization entitled the Global Polio Eradication Initiative was launched. This organization partners with different governmental health organizations to promote vaccine practices that will help to eliminate all forms of the poliovirus, including vaccine-derived polioviruses, which as mentioned above, pose a more serious threat to developing regions than wild-type poliovirus. This means that they are working towards slowly eliminating OPV, so as to replace it with IPV. This is not as simple of a task as it seems though, as the production and manufacturing of IPV are extremely expensive and not a feasible option for developing nations, who often have large populations of children. As a result, researchers have begun to test vaccinations that involve somewhat of a combination of the two vaccinations. The reason IPVs are so expensive to manufacture is that they are created using extremely virulent strains of the vaccine, which pose a great biosafety risk, and are thus expensive to create. Researchers want to create a vaccine that uses less virulent strains of the virus, which are known as Sabin strains, in an inactivated form. However, there is still much more progress that needs to be made before IPV alone can be used to prevent poliovirus in nations where it is endemic.
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