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

UK health authorities are investigating a likely polio outbreak, the first in nearly 40 years.

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

One in 200 infections cause irreversible paralysis, especially in the legs.

But among those paralyzed, 5-10 percent die when their respiratory muscles are immobilized.

The UKHSA said investigators are working “urgently” to determine whether community transmission has occurred.

How was the outbreak identified?

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

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

There are several polioviruses, and they are all highly contagious. They can be transmitted through respiratory droplets but are mainly spread through contact with contaminated feces of contaminated food or water.

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

The Centers for Disease Control and Prevention describes a vaccine-derived poliovirus (VDPV) as a live strain of the attenuated poliovirus initially included in the oral polio vaccine (OPV) and has changed over time to become more like the wild or naturally occurring virus. †

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

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

But isn’t polio nearly eradicated?

Except in Pakistan and Afghanistan, yes, polio has been eradicated. But there is a rise in Africa. And the vaccine that saved the world is somewhat to blame.

It’s an interesting story.

Polio is endemic to dark blue-shaded countries. Image: CDC

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

A more convenient and child-friendly oral vaccine has been developed by Albert Sabin. It was especially useful in developing countries because it didn’t require refrigeration. 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 lollipop water.

However, the Sabin vaccine is made with a live but attenuated virus. Like the live virus, the Sabin vaccine multiplies in the gut and is excreted in the feces.

The problem is that the Sabin vaccine virus has evolved into an entity that causes and prevents the disease.

The shift away from the Sabin vaccine

“Most type 2 poliovirus outbreaks are caused by the vaccine. Then you have a problem where our best weapon is that same vaccine, so you fight fire with fire,” said Dr. Adam Lauring, an associate professor in the Department of Microbiology and Immunology at the University of Michigan.

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

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

Because of its convenience, children in poorer countries still get Sabin’s lollipop water. But it is the weak link in the drive to make the world polio-free.

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 in UK sewage samples each year”.

However, these have “always been one-off findings that were not rediscovered”.

These previous detections occurred “when a person vaccinated abroad with the live oral polio vaccine (OPV) returned or traveled to the UK and briefly shed spores 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, the NHS’s chief nurse in London, said, “most Londoners are fully protected against polio and do not need to take any further action”.

However, the NHS is contacting parents of children under five in London who are of their polio vaccinations, “inviting them to protect themselves”.

According to the World Health Organization, the vaccination rate for several diseases, including polio, in London is about 86.6 percent.

In Australia, 94.9 percent of people have been vaccinated against polio.

Both countries have a shortage. And both have to sort it out.

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