The UK Health Security Agency (UKHSA) has reported the detection of polio virus in several sewage samples from North and East London.
As part of environmental surveillance, sewage samples are routinely tested across the world for the presence of polio virus. As a result, wild polio virus infections are confirmed before any cases of paralysis. Normally, in the United Kingdom, sewage samples demonstrate one to three ‘vaccine-like’ polio viruses each year. However, earlier this month, several samples from a sewage treatment center in northeast London demonstrated the presence of polio virus.
According to the UKHSA press release, researchers collected samples from the London Beckton Sewage Treatment Works between February and June of this year. This covers a population of approximately 4 million people. Samples revealed the presence of the rare vaccine-derived poliovirus (VDPV2). Previously, samples from the same site had shown the vaccine-like type 2 poliovirus (SL2). Bases on genetic analysis, researchers believe that the two virus isolates have a common origin. However, it is unclear what that is.
Moreover, it is important to note that the virus has only been seen in sewage samples and no human cases of polio have come forward in the UK.
99% Reduction in Polio Cases
The poliovirus causes a life-threatening and debilitating condition called poliomyelitis, or polio. Although 90% of people remain asymptomatic or experience a mild infection, remaining can develop the more severe form. This is characterized by numbness, paralysis in the limbs or torso, trouble breathing due to muscle paralysis in lungs, and even death. The disease most commonly affects children under 5 years of age.
There are three types of wild polio virus: type 1, type 2, and type 3. Type 2 and 3 have eradicated across the world. However, wild poliovirus type 1 continues to cause outbreaks in Afghanistan and Pakistan. Thanks to the discovery of the polio vaccine in 1950s, there has been a 99% reduction in polio cases. Widespread vaccination programs and environmental surveillance of the virus has led to countries across the world becoming polio-free. Once endemic in 125 countries worldwide, cases of polio have gone down by 99% since 1988.
The UK reported its last case of wild polio in 1984 and in 2003, the World Health Organization (WHO) declared the country as polio-free. For over two decades, the country has remained free of any polio cases.
In 2020, Africa became the latest polio-free region. All 47 countries in the African region eradicated the endemic virus. However, despite the eradication of wild polio virus, the threat still remains. This is due to outbreaks of circulating vaccine-derived polioviruses (cVDPVs) across the world. Therefore, researchers are working on a new polio vaccine that can provide a coverage against these mutated strains.
Where did the Vaccine-Derived Polio virus (VDPV2) Come from?
Vaccine-derived polioviruses arise due to the mutation of the strain in the oral polio vaccine (OPV). This genetically altered strain can then spread among communities with a low vaccine coverage.
The OPV contains a live virus that replicates in the gut and can passthrough contaminated fecal water to others in the community. While it is harmless to vaccinated children, others living in poor hygiene conditions and with low immunization levels can become infected. Although the vaccine-derived poliovirus is weaker than the wild strain, it can still cause paralysis in unvaccinated individuals. According to WHO, VDPV2 caused 959 cases in 2020.
Therefore, countries across the world have phased out the use of OPV and replaced it with the inactivated polio vaccine (IPV). Britain stopped using OPV in 2004. However, countries such as Pakistan, Nigeria, and Afghanistan continue to administer OPV to control outbreaks. Therefore, it is likely that the case in London came from someone who recently travelled to or visited from one of these countries.
Risk to the Public Remains Low
According to the WHO, polio immunization coverage in London is currently 86.6%. The UK health officials have labelled the risk to public as ‘extremely low’ due to high vaccine coverage in the area. However, in recent years childhood vaccine coverage has decreased in several parts of London. Therefore, parents are urged to check their child’s vaccination status and stay up to date with their polio vaccinations.
Source: UK Health Security Agency