New Delhi: A two-and-a-half-year-old toddler from West Garo district in Meghalaya has been diagnosed with poliomyelitis or polio. The Union government says it’s a case of vaccine-derived polio in an immuno-deficient child (iVDPV), reigniting demands for India to switch to the inactivated polio vaccine (IPV) rather than the oral polio vaccine (OPV).
While polio was eradicated from India in 2011, VDPV — when an individual, mostly children, develops polio after exposure to the weakened poliovirus present in the OPV — has been reported in rare cases. While highly effective, the OPV can cause vaccine-associated paralytic poliomyelitis (VAPP) at a rate of approximately 1 in 2.7 million doses.
“The World Health Organisation (WHO) will soon prepare a detailed report on the polio case confirmed in Meghalaya,” the Union health ministry said this week in response to a query by ThePrint.
Why is it a cause for concern
Typically, a healthy person clears a poliovirus infection within 6 weeks. However, those with primary immunodeficiency (PID), an immune system that does not work properly, who cannot mount an adequate immune response, may have a persistent infection in the intestines, where the poliovirus replicates, and prolonged viral shedding in their faeces.
Cases of iVDPV are generally detected through surveillance for acute flaccid paralysis (AFP) — the sudden onset of weakness or paralysis with reduced muscle tone in children — and poliovirus infections among patients with pelvic inflammatory disease (PID).
The WHO defines iVDPV as a laboratory-confirmed VDPV infection that has a primary humoral (B-cell) or combined humoral and cellular (B- and T-cell) immunodeficiency disorder, i.e., people with compromised immunity and presence of polio virus for a sustained period.
An infection is considered to be persistent if iVDPV is excreted for more than 6 months and such people are at high risk of paralysis or death due to polio.
Before the latest case, a case of VDPV was found in sewage samples in Kolkata in 2022.
The development has again triggered demands that the country should consider phasing out OPV and rely only on inactivated polio vaccine (IPV), administered via an injection, as done by most of the developed countries. Unlike OPV, the IPV, which was introduced in India in 2017, is produced from polioviruses that have been deactivated, so they cannot replicate.
“This is highly concerning because cases of iVDPV run the risk of circulation of the virus in communities, especially among those with low vaccination coverage against polio,” Dr T. Jacob John, professor emeritus at the Christian Medical College, Vellore, and former president of the Indian Academy of Paediatrics.
Highly infectious disease
Polio is a highly infectious disease caused by a virus which invades the nervous system and, in some cases, can cause total paralysis in a matter of hours.
The virus has three main variations, wild poliovirus type 1, 2 and 3 (WPV1, WPV2 and WPV3), and it is transmitted person-to-person mainly through the faecal-oral route or sometimes through contaminated water or food. Initial symptoms are fever, fatigue, headache, vomiting, stiffness of the neck and pain in the limbs.
One in 200 infections can lead to irreversible paralysis (usually in the legs), and among those paralysed, it can be fatal for 5–10 percent whose breathing muscles become immobilised.
India conducts one annual national and two sub-national pulse immunisation campaigns with bivalent (type 1 and 3) OPV (bOPV) for all children below five years, in addition to routine immunisation with five doses — totalling 10 to 15 doses per child depending on the state.
Before April 2016, the OPV administered in the country also included the type 2 poliovirus, but it was later removed since it was globally declared as eradicated since 1999.
In addition to OPV, the injectable polio vaccine is also offered to babies as part of the government’s universal immunisation programme (UIP) at 6 weeks, 4 months, and 16-18 months.
OPV vs IPV: the debate
Since the OPV is administered through the mouth, it triggers the production of antibodies in, both, the intestines and the blood. This means that if a vaccinated person is exposed to the wild poliovirus in the future, the virus won’t be able to replicate and infect other people.
However, the high transmission of this weakened virus can be a problem. In communities where a large number of people have been vaccinated, onward transmission is limited and the poliovirus quickly dies out. However, in areas with low vaccine coverage, this weakened virus may continue circulating for many months, gradually accumulating enough mutations to cause paralysis.
On the other hand, the IPV, while effective at triggering antibodies in the blood — which prevents the virus from travelling to the nerves and causing paralysis — is found to be less effective at triggering antibodies in the intestines. This means that vaccinated individuals can still be infected with wild poliovirus and transmit it to others, even if they don’t become ill themselves.
Gavi, a public-private global health partnership with the goal of increasing access to immunisation in poor countries, has estimated that vaccine-derived polio is extremely rare. Just over 1,000 cases have been reported worldwide among the more than 10 billion doses of OPV that have been administered since 2000.
An infectious disease specialist at the Post Graduate Institute of Medical Education and Research (PGIMER), Chandigarh explained that when a child is immunised with OPV, the weakened vaccine virus replicates in the gut for a limited duration, and as immune system is stimulated, it develops antibodies against the virus.
In areas of crowding and inadequate sanitation, this excreted vaccine-virus undergoes some replication and can spread in the community, which also protects other children through “passive” immunisation.
However, said the PGIMER doctor, if a population is significantly under-immunised, the excreted vaccine-derived virus circulates for a longer time — 12 months or more — and undergoes many genetic changes.
On a few occasions, the vaccine-derived virus genetically changes into a form that causes paralysis similar to the wild poliovirus. It is known as a circulating vaccine-derived poliovirus (cVDPV). Cases of cVDPV have been reported in several countries over the past few years, though not in India.
“iVDPVs, on the other hand, are isolated from people with primary immunodeficiency (PID) in whom the virus continues to replicate due to insufficient immune response,” the PGIMER infectious disease specialist added.
‘Need to completely switch to IPV’
Dr. John underlined that continuing use of the OPV in low- or middle-income countries (LMIC) beyond 1999 because it is cheaper and promises antibodies in the intestine, without ensuring protection from polio with IPV, has resulted in hundreds of kids being paralysed by vaccine-derived polio.
The WHO has flagged this in its Global Polio Surveillance Action Plan and said India was at a high risk of iVDPV.
“Any vaccine is offered to beneficiaries on the basis of risk-benefit analysis when the benefit is higher than the risk — but that is not the case of OPV now — especially since a far safer tool against polio in the form of IPV is available.” Dr. John emphasised.
He also stressed that the risk of a polio outbreak in India could be higher if WPV-2 reaches the country, since it has already been detected in several other countries in Africa and Asia.
(Edited by Sanya Mathur)