Understanding how poliovirus vaccines work and how far we have gone towards the eradication of the disease.

Monday, 01 February 2021

Last cases of wild poliovirus have been detected five years ago in some regions of Africa. The most recent case has been shown to occur in northeast Nigeria. However, since that incident taking place in 2016 up to the present day, no more new cases have been recorded and the World Health Organization (WHO) has declared that Africa is finally free from wild poliovirus. In fact, Africa owed this achievement to a long process of polio-eradication programme, from which a vaccination and immunization programme was developed to prevent the spread of the disease.

Despite such successful achievements in polio-prevention, vaccine-derived virus has still appeared to persist. Indeed, Africa’s fight against the virus seems not to be yet over. Since 2019, about 20 countries worldwide have been reported to have increasing cases of poliovirus due to vaccine-derived polio. 177 cases were estimated to be identified last year in Nigeria, the Democratic Republic of Congo, Central African Republic, and Angola (WHO). This has been, in fact, triggered by lack of further immunization or low immunization rates as still many communities are seen under immunized with poor sanitation, causing a new form of poliovirus. Polio vaccination that includes oral polio vaccine (OPV) can, in some rare cases, be the trigger factor of the outbreak of the virus regardless of how safe and effective the vaccine is. Used in some countries, OPV is done with oral drops which contain an attenuated form of poliovirus that activates an immune response in the body.  When a child is immunized with OPV, the immunity is developed and antibodies are built up; in the meanwhile the vaccine-virus is also excreted. Then, this excreted vaccine-virus can, on rare occasions, spread in under-immunized populations and mutate into a strain that will cause paralysis; this is known as circulating vaccine-derived poliovirus (cVDPV). This is why it is important to continue to vaccinate as many individuals as possible so as to eradicate this deadly infectious disease.

Thus far, two types of poliovirus were found: wild poliovirus (WPV) and circulating vaccine-derived poliovirus (cVDPV).  Wild poliovirus can be defined as an infectious virus invading the nervous system and can cause death and paralysis; whilst cVDPV is a mutated form of WPV, which mostly emerges in under-immunized populations. In fact, there is no cure to poliovirus; yet vaccination remains the safe way to protect children for life. To stop transmission of WPV and cVDPV, countries or communities should be willing to accept to get vaccinated. As such, only two vaccines have been thought to be used to fight against poliovirus: the oral polio vaccine (OPV) and the inactivated polio vaccine (IPV). OPV is the most common vaccine used in some countries, which include African countries; while IPV is known as the only polio vaccine that has been given in the United States since 2000 (CDC). The difference between both vaccines is that IPV is given by shot in the leg or arm and essentially used to maintain population immunity levels as stated by the Global Polio Eradication Initiative (GPEI). GPEI also intends to take on a project aiming at using IPV in other countries.

 

Sources: World Health Organization (WHO) / The Global Polio Eradication Initiative (GPEI) / Centers for Disease Control and Prevention (CDC).

Read 173 times Last modified on Monday, 01 February 2021 09:57
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