It seemed if poliovirus has been completely eradicated from the world, but Pakistan has reported eight new cases of vaccine-derived poliovirus (VDPV) from Khyber Pakhtunkhwa and Punjab provinces. It makes a total 33 cases of poliovirus this year in Pakistan.
Out of these eight new polio cases, six cases are reported in KP province in Peshawar (2), tribal area (1), Bannu (1), Nowshera (1), Lakki Marwat (1) and two cases are reported from Faisalabad city, Punjab.
Before these eight new cases, there were 25 other vaccine-derived poliovirus cases from last year within this country. This is highly unusual to know because vaccine-derived poliovirus (VDPV) is completely eradicated from the whole world and there is no other case since 2016.
Poliovirus is categorized as Type I, II and III polioviruses. A few years ago a vaccine called ‘Trivalent’ was being used against all three types of poliovirus strains. But when Type II poliovirus was eradicated in 2016, a new vaccine ‘Bivalent’ replaced this vaccine. It provided protection from only type I and III viruses as Type II was thought to be eradicated. However, it wasn’t the case and soon some Type II Virus (VDPV) suddenly emerged showing that poliovirus may still exist and all set to bloom.
Normally, an oral polio vaccine or OPV uses a weakened poliovirus which is used to activate the host’s immune system against it. By the time the virus actually attacks the body, the body already has made antibodies against it, thus it doesn’t let it invade it.
When the polio vaccine is given to a child, this weak virus inside the vaccine starts to replicate inside human intestines for some time. It lets the body produce and build antibodies against poliovirus. After that, the virus is excreted from the body.
Sometimes, when an entire population is under-immunized, this excreted poliovirus might spread and infect others, indirectly. If this virus survives for long period, it is much likely to develop itself and mutate into something that is even more dangerous for humans. Sometimes this mutated virus can cause paralysis in a person which is called circulating vaccine-derived poliovirus (cVDPV).
The circulating vaccine-derived poliovirus (cVDPV) outbreaks have been increased by three folds in15 countries during 2018 and 2019. US Centers for Disease Control and Prevention has published 9 poliovirus outbreaks in 6 countries. But cVDPV takes a lot of time to occur.
World Health Organization (WHO) has confirmed that poliovirus still exists though the cases have been reduced by 99% since 1988.
In 2017, there were only 22 reported cases, which were 350 000 in 1988. WHO says that this reduction in cases has been only possible by combined global efforts. This day, only three countries have been a non-stop center for poliovirus cases including Pakistan, Afghanistan, and Nigeria.
Despite this remarkable performance in the last 30 years, if there is still any child who is infected with poliovirus, the health of all children in all countries are at risk of this disease.
It is easy for poliovirus to spread especially from an infected country to a polio-free country. If that happened, it could even spread to all unimmunized populations. If poliovirus failed to get eradiated, within a few years it would be all over again. WHO explains there is no cure for poliovirus and it could only be controlled through control and prevention techniques. Only multiple shots of the Polio vaccine can protect all children from vaccine-derived poliovirus (VDPV).