Polio vaccine for Covid-19 ‘testable’, may offer limited protection: Report
With a vaccine for Covid-19 at least a year away, scientists say repurposing already safe and effective vaccines is the way to go for immediate relief against Covid-19.Updated: Jun 18, 2020, 18:47 IST
Indian scientists have responded cautiously to a suggestion by global researchers that the oral polio vaccine be tested for Covid-19 treatment, saying it is a “testable idea” based on a sound scientific concept but may offer only limited protection against the infection.
With a vaccine for Covid-19 at least a year away, scientists say repurposing already safe and effective vaccines is the way to go for immediate relief against Covid-19. The repurposed vaccines could include the oral polio vaccine (OPV) and the Bacillus Calmette–Guerin (BCG) used against tuberculosis, both part of the immunisation given to Indian children.
It is worth conducting a clinical trial, said Ram Vishwakarma, director of the CSIR-Indian Institute of Integrative Medicine (CSIR-IIIM) in Jammu.
He was responding to a study last week by an international team of researchers in the journal Science. The researchers, including Shyamasundaran Kottili and Robert Gallo from the University of Maryland School of Medicine in the US, said the OPV should be tested to see if it might protect people from the SARS-CoV-2 virus.
They noted that the vaccine used to prevent poliomyelitis infections has been around since the 1950s, and is found to provide some protection against other viral infections.
The stimulation of innate immunity by attenuated vaccines -- live but with substantially reduced virulence -- in general and OPV in particular could provide temporary protection against Covid-19, the scientists noted.
Innate immunity is one of the two main immunity strategies found in vertebrates, including humans.
According to Vishwakarma, the idea proposed by Gallo, an internationally renowned virologist who co-discovered that HIV causes AIDS, is based on the fact that people who have undergone polio vaccination boost their innate immunity.
“It is a sound scientific concept but we do not know what will eventually happen because this has multiple phases. It may help patients in the early phase, with mild and moderate symptoms but may not help serious patients,” Vishwakarma told PTI.
“It is a testable idea based on a scientific hypothesis that is in turn based on the concept of what we call trained immunity, a non-specific way to boost innate immunity for our immune system to fight out the virus,” Vishwakarma explained.
India has been implementing a pulse polio programme since 1995 with an aim to eradicate polio, added virologist Upasana Ray. This is in accordance with a resolution passed by the World Health Assembly in 1988 for polio eradication globally.
“Every year, children between 0-5 years age are immunised with polio vaccine. It is a very widespread and well established programme,” Ray, senior scientist at CSIR-IICB, Kolkata, told PTI.
Immunologist Satyajit Rath added that it is best to keep in mind that Gallo and his team are not talking about the function of the OPV as a ‘vaccine’ which generates a specific immune response.
“Instead, it is simply the idea of giving people a viral infection, any viral infection, so that there is activation of innate antiviral and inflammatory immunity, which might reduce the chances of another virus (SARS-CoV-2) infection which enters at the same time,” Rath, from the National Institute of Immunology (NII) in New Delhi, told PTI.
“Do I think this might work? It might, to some very modest extent, would be my guess, and not enough to make it particularly worthwhile,” he said.
Noting that repurposing vaccines is a good idea, Ray said there is a chance of cross protection to some extent if the proteins of two pathogens have similar sequences even at some epitopes.
An epitope is a part of an antigen or a foreign substance that is recognised by the immune system cells, specifically by antibodies, B cells and T cells.
“For polio also, we first need to see if any of the polio proteins show overlapping T or B cell epitopes as compared to that of SARS-COV-2. If there are, it might provide some protection... To what extent? That needs validation,” said Ray.
Vishwakarma said the Council of Scientific & Industrial Research (CSIR) is currently testing a repurposed vaccine against Covid-19 on the similar lines of a polio vaccine.
It is testing Cadila Pharmaceuticals’ Sepsivac against Covid-19 in a Phase 2 clinical trial.
This immunotherapy treatment, which boosts “innate immunity”, has been approved by the Drug Controller General of India (DCGI) for clinical trials, he said.
Rath noted that there are major potential limitations to using the polio vaccine for Covid-19.
First, it is likely that this ‘protection’ by ongoing innate immune activation is likely to be of short duration.
Second, the likelihood is that a lot of people in India, particularly children, are immune to polio, and therefore will not actually let the OPV ‘work’ as an infection, he said.
“Instead, polio-immune individuals would be ‘protected’ against yet more vaccine, which would defeat the SARS-CoV-2-related purpose,” Rath noted.
“In fact, even amongst those who do not have current anti-polio antibodies, this ‘protection’ would likely be a transient one-time effect for a few days which is unlikely to be repeatable since this first exposure would make them polio-immune,” he said.
Agreeing with Rath, Ray noted that most people in India are already vaccinated against polio in childhood.
“Aren’t those people getting infected? Say yes, still they are.......then the next question could be, are they getting sick similar to non-vaccinated ones?” she said.
“Next, is it possible that for polio it is providing life-long protection. Is it possible that in case some epitopes are matching that vaccination could help? All these are blind spots. Need time testing,” said Ray.