It has been nearly 40 years since the United Kingdom discovered its last outbreak of poliovirus, an infection feared for its ability to leave patients paralyzed and crippled.
Thanks to extensive vaccination efforts around the world, the disease has been largely eliminated. Afghanistan and Pakistan are the only two remaining countries in the world where polio is still classified as endemic.
But outbreaks remain common – and now the UK has become the last country to report what appears to be a recurrence of the deadly disease.
Here’s what we know:
How many cases have been detected?
It is not clear at this stage. In a statement issued Wednesday, the UK’s Health Security Agency (UKHSA) said the virus had been identified in sewage samples taken from London between February and May 2022.
The agency said the virus was “likely” to spread among “closely linked” people in north-east London, and an investigation was launched to determine if there was any transmission from the community.
No suspicious cases have been reported or confirmed so far. No related cases of paralytic polio have been reported.
The samples were taken from London’s Beckton Sewage Works, which covers a population of approximately four million people.
What do we know about virus testing?
The analysis shows that the virus accepted by the UKHSA is not wild-type polio. Instead, it is a version of the virus that comes from a live oral polio vaccine (OPV).
Live OPV is used in poorer parts of the world to respond to outbreaks of polio. This vaccine generates intestinal immunity and a few weeks after vaccination, people can excrete the vaccine virus in their faeces.
These vaccine viruses can then spread to communities with insufficient human-to-human vaccination through poor hand hygiene and contamination of water and food. Coughing and sneezing, although less common, are another route of transmission.
As it appears to have been spreading in the UK for several months, the virus may mutate into a vaccine-derived version of the poliovirus, which behaves more like the naturally occurring ‘wild’ type.
These strains of the virus are known to be vaccine-produced poliovirus type 2 (VDPV2), which the UKHSA has detected in wastewater samples in London.
How is polio spread?
The virus is spread in communities with low human-to-human vaccination through poor hand hygiene and contamination of water and food. Coughing and sneezing, although less common, are another route of transmission.
It is estimated that 95 to 99 percent of people who become infected with poliovirus are asymptomatic. Even without symptoms, people infected with poliovirus can still spread the virus and cause infection in others.
In the case of the United Kingdom, the virus derived from the vaccine appears to have been introduced earlier this year and began spreading between February and May.
The virus was probably introduced into the United Kingdom by a person vaccinated with OPV in an overseas country. From then on, it may have spread within a family.
“These findings suggest that there may be a localized spread of poliovirus, most likely among people who are not up to date with polio immunizations,” said Dr. Kathleen O’Reilly, an associate professor of infectious disease statistics.
How dangerous is polio?
Most people infected with the virus (about 72 out of 100, according to the US Centers for Disease Control and Prevention) will not develop any visible symptoms, which means that the infection comes and goes without harm.
About 1 in four will have flu-like symptoms such as sore throat, fever, fatigue, nausea, headache and stomach pain. They usually last from 2 to 5 days.
Fewer people (1-5 in 1,000) with poliovirus infection will develop other, more serious symptoms that affect the brain and spinal cord, leading to paralysis in some cases.
Paralysis is the most severe symptom associated with polio, as it can lead to permanent damage and death. Between 2 and 10 out of 100 people who are paralyzed by a poliovirus infection die because the virus affects the muscles that help them breathe.
Even children who appear fully recovered may develop new muscle pain, weakness, or paralysis as adults 15 to 40 years later. This is called post-polio syndrome.
How does polio stop?
Vaccination is the most effective way to reduce community transmission and protect people.
The United Kingdom switched from the use of OPV to inactivated polio vaccine (IPV) given by injection in 2004. The vaccines are given with routine NHS vaccines for children at 8, 12 and 16 weeks as part of the 6-in-1 vaccine. offer at three and 14 years.
The last case of wild polio in the United Kingdom was confirmed in 1984, and the United Kingdom was declared free of the virus in 2003. Afghanistan and Pakistan are the only two countries in the world where the infection is still classified as endemic. Both nations rely on OPV for their immunization programs.
Add Comment