ISLAMABAD: As many as six cases of vaccine-derived polio virus (VDPV) have been confirmed and the victims belong to different areas of Khyber Pakhtunkhwa (KP) and Punjab.

This type of poliovirus was officially declared eradicated across the globe in 2016. According to experts, it is almost impossible to determine from where the virus leaked and started spreading, but it has reached over 20 countries and again become a threat to mankind due to its ability to mutate.

However, National Manager of the Emergency Operation Centre for polio, Dr Rana Safdar, said though this virus could paralyse children, it was not as aggressive as wild poliovirus. He also claimed this virus would be controlled in Pakistan soon.

There are three types of poliovirus which are categorised as Type I, II and III. Decades ago a vaccine named ‘Trivalent’ was used which contained all the three viruses. After eradication of Type II Virus in 2016 another vaccine, ‘Bivalent’, was introduced. It contained only type I and III viruses. However suddenly cases of Type II Virus (VDPV) are being reported and it is feared that the virus can re-emerge.

The virus was declared eradicated across world in 2016

An official of the National Institute of Health said that all VDPV cases of the year 2020 had been reported among children aged between one and two-and-a-half years. “It means that all of them were born after discontinuation of use of the Type II vaccine.

Among the six cases of the VDPV, five cases have been reported from KP and one from Punjab. Among the victims from KP, four children have been infected in Khyber district, including three boys aged 14, 13 and 19 months and a 25-month-old girl. The fifth victim from the province is a 31-month boy, resident of Nowshera. In Punjab, a 13 months old girl, resident of Rawalpindi, has been infected with Type-II Virus (VDPV),” the official said.

“As after detection of such cases, Monovalent vaccine (mOPV2), having only Type II Virus, is given so in Khyber, one round of the mOPV2 campaign was conducted on Jan 29-Feb 4, while two more rounds are planned in March. In Nowshera, two rounds of the mOPV2 campaign were conducted in January. In Rawalpindi, two rounds of the mOPV2 campaign were conducted in Nov 2019,” he said.

Replying to a question, the official said that last year, 25 cases of Type II Virus (VDPV) were reported from across the country and during current year so far nine cases had been reported.

According to information available on the website of the World Health Organisation (WHO), oral polio vaccine (OPV) contains an attenuated (weakened) vaccine-virus, activating an immune response in the body. When a child is immunised with the OPV, the weakened vaccine-virus replicates in the intestine for a limited period, thereby developing immunity by building up antibodies. During this time, the vaccine-virus is also excreted. In areas of inadequate sanitation, this excreted vaccine-virus can spread in the immediate community (and this can offer protection to other children through ‘passive’ immunisation), before eventually dying out.

On rare occasions, if a population is seriously under-immunised, an excreted vaccine-virus can continue to circulate for an extended period of time. The longer it is allowed to survive, the more genetic changes it undergoes. In very rare instances, the vaccine-virus can genetically change into a form that can paralyse – this is what is known as a circulating vaccine-derived poliovirus.

University of Health Sciences Vice Chancellor Dr Javed Akram, said: “Research is needed to control this virus but there is a huge gap between academia and policy makers. Unfortunately no one prefers to speak on such issues which cannot be addressed without taking the academia into confidence.” He stressed the need to analyse the quality of polio vaccines, immunity level of children and acceptability of vaccine in society.

Dr Safdar, while talking to Dawn, said that cases of Type II Poliovirus (VDPV) had been reported in more than 20 countries, including China, Philippine, Indonesia, Malaysia and Nigeria.

“There were more chances of mutation in Type II Poliovirus so Trivalent vaccine was discontinued and in 2016 Bivalent vaccine was introduced. Type II Virus can be eradicated by one or two good rounds of vaccination and this is why we have arranged the mOPV2 vaccine which is nowhere available, apart from WHO head office in Geneva, to ensure that the virus would not spread in the environment”.

He said that a new mOPV2 vaccine, which had lesser chances of mutation of the virus, had been experimented in Bangladesh and hopefully would be introduced in Pakistan by June this year.

“Strengthening routine immunisation is another critical intervention as many countries, including Pakistan, administer one dose of injectable polio vaccine that also has Type II component and generates immunity against it. Pakistan is maintaining very strong surveillance to detect the VDPV and pursues standard guidelines to tackle all new detections with mOPV2 response that is based on thorough risk assessment,” Dr Safdar said.

Published in Dawn, February 24th, 2020