In the UK, traces of the highly contagious polio virus have been found in the sewers of London. Repeated positive tests for polio suggest there is ongoing infection and likely transmission in the area. That’s unexpected, as the UK has been declared polio-free since 2003. Here’s the takeaway.
Just when we thought ‘monkeypox’ would be the new virus of 2022, the UK Health Security Agency (UKHSA) said repeated detections of the polio virus had been made in sewage in the north and east. east of London.
Poliomyelitis (polio) is a devastating disease that has historically caused paralysis and death around the world. It is caused by small RNA viruses that can damage cells in the nervous system. There is no cure for polio (also called infantile paralysis). We can only treat the symptoms.
It is not present in animals and, like smallpox, it can be eradicated. And thanks to effective vaccination campaigns, we are getting closer to this goal every year.
Three types of polio
There are three types of polio virus, and infection or immunization with one type does not protect against the other. Type 1 virus continued to cause epidemics, but transmission by types 2 and 3 was successfully interrupted by vaccination.
The virus is transmitted by airborne droplets, but it can also be contracted from food or water that has come into contact with the stool of a person with the virus. This can survive for several days at normal temperatures.
Recent outbreaks have been linked to areas with poor sanitation and where vaccines are difficult to deliver. Afghanistan and Pakistan are the only two countries where “wild” polio is still endemic and where eradication programs are in place to prevent the spread of the virus to other countries.
Two vaccines
Vaccines played a crucial role in the eradication of polio. In 2021, there were less than 700 reported cases worldwide.
In our region, we use injected poliomyelitis vaccine. It contains inactivated virus (IPV) and is safe and effective in protecting the immune person against polio, but is less effective in inducing local immunity in the gut, so vaccinated people can still become infected and transmit the virus. infectious virus even if they do not show symptoms themselves.
IPV provides excellent protection for the individual, but is not sufficient to control an outbreak in poor sanitary conditions. The oral poliomyelitis vaccine (OPV), which contains a live but attenuated virus, is much more interesting in this situation. OPV is administered in the form of drops and does not require trained personnel or sterile equipment to administer, so it can easily be provided to isolated populations.
This vaccine can induce strong intestinal immunity and it can prevent the spread of the virus. As it contains live virus, it can spread to close contacts of the immunized person and protect them as well. It is also less expensive than VPI.
VDPV type 2
The downside of using OPV is that the weakened virus can mutate and, in rare cases, revert back to a crippling variant.
OPV is cleared by our immune system within days, but this may not be the case in people with weakened immune systems who may carry the virus for longer, increasing the risk of mutations. In countries with insufficient immunity, this can result in the circulation of vaccine-derived virus (VDPV). The virus detected in the London sewer was indeed of the vaccine-derived variety, VDPV type 2.
This “mutant” form of polio can cause asymptomatic infection in people vaccinated with IPV, and it is excreted in the faeces because there is no local intestinal protection in IPV. It can therefore be detected in wastewater.
Detection methods are sensitive, but a single positive reading would not be alarming. VDPV type 1 was also recently detected in sewage from Calcutta, India. It is believed to have originated from an imported case of a vaccinated person with a weakened immune system who was unable to clear the vaccine strain from their body.
Mandatory in our country
The detection in London suggests it is likely that ‘there has been some spread between closely related individuals in north and east London and they are now shedding the type 2 poliovirus strain in their faeces “, according to the British health service. She says she normally detects between one and three “virus isolates per year” in wastewater, but these are normally single, unrelated isolates. In this case, isolates identified between February and June 2022 are genetically linked. The most likely scenario is that a recently vaccinated person entered the UK from a country where an oral polio vaccine was used.
In principle, there is no problem for our country: vaccination against polio is the only legally compulsory vaccination in Belgium. Parents must provide proof of complete vaccination to the municipality no later than when their child reaches the age of 18 months. People who come from countries where the disease is still endemic are also offered polio vaccination when they arrive in Belgium if they were not vaccinated when they left the country. This is World Health Organization advice that also applies to adults.
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