Demystifying vaccine-derived Polio virus concerns

The Government of Telangana has called for a polio immunisation drive from June 20 to June 26 and has put the officials of health department on high alert after a vaccine-related polio virus was found and collected from sewage in Amberpet, Hyderabad

In a mass vaccination drive, more than three lakh children in the city and parts of Ranga Reddy district will be inoculated as a preventive measure. Two lakh vaccines were airlifted from Geneva immediately after the virus was detected.

India continues to be polio free, the government said in a statement released. The country has eradicated the wild polio virus and the last case was seen more than five years ago and later no wild polio virus was detected.

However, samples which were collected from nala tested positive for polio and found Type -2 vaccine derived polio virus (VDPV). Vaccine derived polio viruses are rare strain of the polio viruses that have genetically mutated from the strain contained in the Oral Polio Vaccine (OPV).

Here are five things to know about vaccine-derived polio virus (VDPV) and the concerns around it as listed by the authorities:-

What is polio?
To demystify, Poliomyelitis or polio is a highly infectious disease caused by a virus that invades the nervous system, and causes paralysis, medically known as an acute flaccid paralysis (AFP), which is characterised by sudden muscle weakness and pain in the limbs. The disease is transmitted from person to person, mainly through the faecal-oral route, affecting children under five years of age. In the absence of wild polio virus (WPV) transmission, India was declared a polio-free country in March 2014, after years of relentless vaccination.

What samples collected reveals?
Generally, World Health Organization (WHO) conducts surveillances for cases of AFP and collects samples of sewage water to find any traces of polio viruses, in order to the maintenance of polio eradication in polio-free countries. In one of such cases in Hyderabad, out of samples collected, one from Amberpet nala contained traces of type-2 VDPV. Even lab tests have also confirmed that the virus has passed through human body and has undergone mutation or nucleotide change. Similar virus strains were detected in Delhi, Bihar and Gujarat. The Telangana government has advised the people not to panic and called for a one-week special polio immunisation drive in Hyderabad to vaccinate around 3,00,000 children.

What is a vaccine-derived polio virus?
Vaccine derived polio virus means the source of the virus is the vaccine itself. The oral polio vaccine usually called polio drops, which India deployed extensively to fight against polio, contained a live attenuated or weakened polio virus. When a child is vaccinated, the weakened vaccine-virus replicates in the intestine and enters into the bloodstream, triggering a protective immune response in the child.

Like wild polio virus, the child excretes the vaccine-virus for a period of six to eight weeks. Importantly, as it is excreted, some of the vaccine-virus may no longer be the same as the original vaccine-virus as it gets genetically altered during replication. In areas of inadequate sanitation, this excreted vaccine-virus can quickly spread in the community and infect children with low immunity.

Is VDPV a concern?
The chances of paralysis due to VDPV are rare as the virus has to circulate for a long time in the community of under-immunised population before it can infect and cause paralysis in someone. Vaccine-associated paralytic poliomyelitis (VAPP) occurs in an estimated 1 in 2.7 million children receiving their first dose of oral polio vaccine, according to the Global Polio Eradication Initiative, a public-private partnership of national governments and WHO.

The aspect that is a matter of concern is that India reports high number of non-polio—AFP or paralytic—cases in children who are less than 15 years of age, which the study links to the VDPV. In India more than 50,000 AFP cases are being investigated every year as a part of surveillance system, according to WHO.

What is Oral Polio Vaccine and Inactivated Polio Vaccine?
Generally, Oral Polio Vaccine (OPV) is being administered in Hyderabad, but the detection of VDPV has emerged a discussion on replacing the OPV with Inactivated Polio Vaccine(IPV), while IPV is administered through an injections containing inactivated virus, which is considered to be safe than OPV as it contains live virus.

Even, the World Health Organisation has also been advocating IPV over OPV as part of its global endgame strategy on polio eradication completely. But India introduced the IPV as mandatory in immunization on December 1, in six states only. For the time being IPV will be given in addition to the existing OPV, as it suits to the country like India due to its low cost, high efficiency and ease of administering, and argue that the safety concerns are overstated compared to the benefits of the vaccine.

By Gudipati Rajendera Kumar