In Depth

How the polio vaccine could curb coronavirus

Scientists hope the decades-old vaccination may provide protection against a second wave of Covid-19

A vaccine developed in 1952 and delivered to generations of children on lumps of sugar could become the first line of defence against Covid-19, new research suggests.

Scientists from the Global Virus Network (GVN) say the vaccination against poliomyelitis, commonly known as polio, “could provide temporary protection” from the new coronavirus.

The childhood immunisation is the second of its kind to be identified as a possible weapon against the ongoing pandemic, with large-scale trials already under way to test whether the BCG vaccine for tuberculosis could be used to tackle the health crisis.

“If shown effective, those vaccines could potentially provide protection against the second wave of coronavirus, which is likely to crest before a covid-specific vaccine is widely available,” says The Washington Post.

The polio hypothesis

Like the BCG jab, the polio vaccine consists of a weakened - but still live - strain of the disease.

This “is expected to trigger a general immune response to any foreign organism”, during which the recipient develops antibodies to fight the specific virus or bacteria introduced into their body, says Forbes.

And such vaccines may have a useful secondary effect.

“An increasing body of evidence suggests that live attenuated vaccines can also induce broader protection against unrelated pathogens,” write researchers from the GVN, a coalition of medical virologists, in a paper published in the journal Science.

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“A retrospective study from Denmark found that the use of OPV [oral polio vaccine] was associated with reduced hospital admissions for respiratory infections in children,” they add. 

There is no evidence as yet that the polio vaccine works specifically against the new coronavirus, but the researchers are calling for immediate trials to test their theory.

Reasons for caution

Few medical interventions come without risks, and the polio vaccine is no exception.

In fact, the live oral vaccine “is actually being phased out” and replaced with an inactivated version, delivered by injection, says Dr Peter Hotez, dean of the US National School of Tropical Medicine.

This switch is partly because the live vaccine can lead to a full-blown case of polio in a small number of cases, and partly because even people who are successfully immunised will shed traces of live polio in their faeces. Once in the sewage system, the virus could enter the water supply.

“I think OPV is worth studying,” Hotez told Forbes, “but this has to be weighed against the risk of re-introducing live strains.”

Widespread vaccination has eliminated polio from all but two countries, Pakistan and Afghanistan, where the coronavirus pandemic is hampering eradication efforts. “In April, almost 40 million children missed their polio drops in Pakistan after the cancellation of the nationwide vaccination campaign,” The Guardian reports. 

Most people infected with polio make a full recovery, but the virus can lead to muscle weakness, paralysis and death by suffocation in a small minority of cases.

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