UK’s first polio outbreak in 40 years: how it happened

British health authorities are investigating a probable polio outbreak, the first in nearly 40 years.

The UK Health Security Agency (UKHSA) has yet to directly identify cases of this devastating disease which mainly affects children under the age of five.

One in 200 infections causes irreversible paralysis, mainly in the legs.

But among the paralyzed, 5 to 10% die when their respiratory muscles are immobilized.

The UKHSA said investigators were working “urgently” to establish whether there was community transmission.

How was the outbreak identified?

The investigation was launched after “several closely related viruses were found in sewage samples taken between February and May”.

There are a number of poliomyelitis viruses and they are all highly contagious. They can be transmitted by respiratory droplets, but spread mainly through contact with infected feces containing contaminated food or water.

In this case, the virus identified at the London Beckton Sewage Treatment Works is ‘vaccine-derived’ poliovirus type 2 (VDPV2).

Centers for Disease Control and Prevention describe a vaccine-derived poliovirus (VDPV) as a live strain of the weakened poliovirus that was originally included in the oral polio vaccine (OPV) and which has changed over time to behave more like the wild or natural virus.

The UKHSA said the detection of a VDPV2 made it “likely that there has been some spread between closely related individuals in north and east London and they are now clearing the type poliovirus strain 2 in their faeces”.

Dr Vanessa Saliba, consultant epidemiologist at UKHSA, said: “Vaccine-derived poliovirus is rare and the risk to the general public is extremely low.”

But isn’t poliomyelitis about to be eradicated?

With the exception of Pakistan and Afghanistan, yes, poliomyelitis has been eradicated. But there has been an emergence in Africa. And the vaccine that saved the world is somewhat to blame.

It’s an interesting story.

Polio is endemic in countries shaded dark blue. Image: CDC

The original vaccine developed in 1955 by Jonas Salk was an inactivated (killed) polio vaccine (IPV) and given by injection.

A more practical and child-friendly oral vaccine was developed by Albert Sabin. It was particularly useful in developing countries because it did not need to be refrigerated. And there were no needles involved.

Sabin’s oral vaccine arrived in Australia in 1966 and was then routinely given to children at school as a few drops of what tasted like a lollipop.

However, the Sabin vaccine was made with live but weakened virus. Like the live virus, the Sabin vaccine multiplies in the intestine and is excreted through the faeces.

The problem now is that the Sabin vaccine virus has become an entity that both causes and prevents disease.

The abandonment of the Sabin vaccine

“Most type 2 polio outbreaks are caused by the vaccine. Then you have a problem where our best weapon is that same vaccine, so you’re fighting fire with fire,” said Dr. Adam Lauring, associate professor in the University of Michigan’s department of microbiology and immunology.

In 2020Dr. Lauring and his colleagues conducted a study that allowed them to see the evolution of the vaccine virus into a more dangerous form.

This is actually old news. The Western world has been moving away from the live Sabin vaccine since the turn of the century. Australia switched from the oral vaccine to an inactivated polio vaccine in November 2005.

Children in poorer countries continue to receive water from Sabin’s pacifier, for convenience. But it is the weak link in the effort to free the world from polio.

Back to London

According to the UK Health Security Agency, as part of routine surveillance, it is “normal for one to three ‘vaccine-like’ polioviruses to be detected each year in UK sewage samples”.

However, these were “still point finds that have not been detected again”.

These previous detections occurred ‘when a person vaccinated overseas with the live oral polio vaccine (OPV) returned or traveled to the UK and briefly passed traces of the vaccine-like poliovirus in their stool “.

The last case of wild polio contracted in the UK was confirmed in 1984. The UK was declared polio-free in 2003.

Jane Clegg, NHS chief nurse in London, said “the majority of Londoners are fully protected against polio and will not need to take any further action”.

However, the NHS is reaching out to parents of children under five in London who are not up to date with their polio vaccinations “to urge them to protect themselves”.

According to the World Health Organization, vaccination coverage for several diseases including poliomyelitis in London is around 86.6%.

In Australia, 94.9% of the population is vaccinated against poliomyelitis.

Both countries have a deficit. And the two have to work out.

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