Islamabad: Pakistan’s vaccination program has come under suspicion after poliovirus was detected in sewage samples in London for the first time in four decades, according to a media report on Friday.
The UK Health Security Agency noted that the virus detected on Thursday was likely imported from a country and urged parents to ensure their children were fully immunized against the crippling disease.
Health authorities in Islamabad say the vaccine-derived virus found in the UK exists in 22 countries and the type found locally was wild poliovirus (WPV).
The national coordinator of Pakistan’s polio eradication programme, Dr Shahzad Baig, told the Dawn newspaper on Thursday that it was too early to say the virus had traveled from Pakistan, as British authorities had no yet announced the results of genome sequencing.
Genome sequencing helps determine the origin of a virus because samples detected in different areas have different ribonucleic acid (RNA). On several occasions, cases reported in Pakistan originated from neighboring Afghanistan during genome sequencing.
We are awaiting the virus genetic sampling report. In addition, there are two types of poliovirus in the world: PVS which is present in Pakistan and Afghanistan, and vaccine-derived poliovirus (VDPV).
Environmental samples in London turned out to be VDPV, which exists in 22 countries, so Pakistan should not be blamed for exporting it before receiving the genetic sequencing report, Baig said.
He said the vaccine-derived variety may have traveled from Nigeria, Egypt, Pakistan, Afghanistan, Yemen, Sudan, Central Africa and a number of other countries.
An expert from the Department of National Health Services, who was not authorized to speak officially, said there were three types of VPS, according to the report.
Decades ago, a vaccine called Trivalent’ was used because it contained all three types. After type II eradication in 2016, a bivalent vaccine was introduced with WPV types I and III.
However, in 2020 type II suddenly reappeared due to which it was feared that the virus had the potential to resurface. This second type of virus is called VDPV because it has been totally eradicated from the world, he said.
The oral polio vaccine (OPV) contains an attenuated (weakened) vaccine virus, activating an immune response in the human body. When a child receives OPV, the weakened vaccine virus replicates (grows) in the intestine for a limited period, thereby developing immunity by accumulating antibodies, the expert said.
During this time, the vaccine virus is also excreted. In areas with inadequate sanitation, this excreted vaccine virus can spread within the immediate community (and offer protection to other children through passive immunization), before eventually disappearing, he said. .
On rare occasions, if a population is severely underimmunized, shed vaccine virus may continue to circulate for an extended period. The longer it is allowed to survive, the more genetic changes it undergoes.
In very rare cases, the vaccine virus can genetically change into a form that can cripple this is called circulating vaccine-derived poliovirus, the expert explained.
Dr Nadeem Jan, a public health expert, said Pakistan would be in a difficult, rather embarrassing situation if the virus found in London was proven to have traveled from here.
Pakistan has already been subject to a travel advisory under which every person must be vaccinated and carry a vaccination certificate before traveling abroad. We also affirm that the vaccination target of more than 90% has been achieved. The world might doubt our claims if the virus turns out to belong to Pakistan, he noted.
Dr Baig, while answering a question, said the poliovirus was generally under control in Pakistan, except in North Waziristan where there were vaccine refusals and people were not cooperating with polio teams.
About 200 countries have already eradicated the virus, and Pakistan can also reach the goal. Unfortunately, North Waziristan has become a haven for the virus, but if we are able to defeat the virus there, we can eradicate it from the country, he said.
Pakistan and Afghanistan are the only two remaining polio-endemic countries in the world after Nigeria was declared poliovirus-free in 2020.
The Pakistani government had to suspend the polio campaign in the past following an increasing number of attacks on polio workers in different parts of the country.
Attempts to eradicate the debilitating disease have been seriously hampered by the deadly targeting of vaccination teams in recent years by activists, who oppose the campaigns, claiming polio drops cause infertility.
Read also : Principal IPS Tapan Kumar Deka appointed new IB chief