Oral Poliovirus Vaccine Drop Contamination: What We Need To Know About Type 2 Polio
Oral poliovirus drops (Photo Credits: Flickr, RIBI Image Library)

Ever since 1.5 lakh vials of contaminated oral poliovirus (OPV) drops have been detected in Telangana, Maharashtra and Uttar Pradesh, India’s polio situation have started to look rather grim. The central government swung into action when an eradicated strain of the type 2 poliovirus was detected in stool samples of children in Uttar Pradesh. The strain was traced to vials of trivalent OPVs manufactured and supplied to the government by a Ghaziabad firm Bio-Med. Two years since type 2 poliovirus was phased out by the Indian government, Bio-Med was still manufacturing and supplying them. Panic has gripped the nation and already misleading WhatsApp forwards warning parents against vaccinating their children are doing rounds. If you are new to the issue, here’s why the detection of type 2 poliovirus is a cause for concern.

What is An Oral Poliovirus?

OPV is an oral vaccination given to children. It contains a weakened strain of vaccine-virus, which activates an immune response in the body. An OPV can contain one strain of the virus (monovalent), two strains (bivalent) or three strains (trivalent.) When OPV is given to the child, the body produces antibodies in the blood and in the intestines to fight the weakened strain of the virus.

These antibodies produced in the human body aids in stopping the ability of the virus to replicate or spread to others. During this time, the vaccine-virus is shed through the stools. In areas which lack in sanitation, the virus gets exposed to other children, offering passive immunisation before it dries out eventually.

Before India achieved its “Polio Free” status, trivalent OPVs were being given to children, which contained strains of type 1, 2 and 3 of poliovirus. But after type 2 poliovirus was completely eradicated, only bivalent polio drops were administered, which contained only type 1 and type 3 of poliovirus.

What Should We Know About Poliovirus Type 2?

Poliovirus type 2 has not been detected anywhere in the world after October 1999. Given the excellent polio surveillance system, it can be believed that polio type 2 has been eradicated globally. Since it is no longer in the world, WHO instructed that the type 2 virus should be dropped from the trivalent polio drops.

Vaccine viruses like type 2 poliovirus are weaker than their wild variants. Their capacity to attack the human nervous system and spread is reduced. But these vaccine viruses also tend to mutate, which can increase their neurovirulence (ability to affect the nervous system). Will Polio Return to India? Contaminated Vaccines Raise Concerns That the Eradicated Disease May Strike Again.

But in rare situations, when the population is under immunised, the excreted virus-vaccine in the OPV continues to circulate in the body for an extended period. The longer it survives outside, the more genetic changes it can cause. Rarely, it can mutate into a form that can cause paralysis. This is called circulating vaccine-derived poliovirus (cVDPV) which causes vaccine-associated paralytic polio (VAPP).

If these mutated viruses are shed through stools, it can infect other children in areas with reduced immunisation coverage. It could then result in the spread of cVDPVs.

In 2013, the Global Polio Eradication Initiative devised the Polio Eradication and Endgame Strategic Plan 2013-2018, which called for the phased removal of OPVs. In phases, one by one, all the three vaccine viruses will be removed, beginning with “the switch”, where trivalent OPV will be replaced bivalent OPV. In keeping with the plan, India had already stopped doling out trivalent OPVs containing type 2 poliovirus.

With the detection of the eradicated type 2 poliovirus, alarm bells have rung out in the medical community, raising fears of viral mutation and VAPP.

Is There A Need To Panic?

While it is a scary situation, WHO has allayed any fears of a renewed polio infection, saying that any risks caused by the exposure to type 2 poliovirus will be minimal. That’s because India has high routine polio immunisation coverage, which will ensure that the viral exposure may not cause much harm.

Dr Santosh T Soans, President of the Indian Academy of Pediatrics (IAP) assures that the governmental agencies have taken prompt actions. The use of bivalent OPVs supplied by Bio-Med to the governmental vaccination programme has been stopped.

“Later, Central Drug Standard Control Organization, Directorate General of Health Services, Ministry of Health and Family Welfare, New Delhi, the drug and vaccine regulator, stopped manufacture, sale and distribution of bOPV by Biomed (P) Ltd,” adds Dr Soans.

He states that the coverage of eligible population of IPV or Inactivated Polio Vaccine (administered through injection) is quite good in India. The immunity of people against type 2 poliovirus is quite strong.

“Further, the polio surveillance system in India is also very strong and sensitive,” he says. The robust system set in place by the Indian government will pick up on any aberration and check on the spread of poliovirus very early.

Parents need not panic. “The immunisation against polio should continue as per the IAP immunisation schedule. Both the vaccines, IPV and the bivalent OPV, are safe for use and should be continued,” adds Dr Soans.