What you need to know about the disease

Birmingham, United Kingdom:

Just when we thought monkeypox would be the new virus scare of 2022, the UK Health Security Agency (UKHSA) declared a national incident of repeat poliovirus detection in sewage in north and east London. Repeated positive readings for polio suggest there is ongoing infection and probable transmission in the region. This is unexpected given that the UK has been declared polio-free since 2003. Here’s what you need to know.

Poliomyelitis (polio) is a devastating disease that has historically caused paralysis and death worldwide. It is caused by polioviruses, small RNA viruses that can damage cells in the nervous system.

It does not occur in animals and can therefore be eradicated like smallpox. And thanks to effective vaccination campaigns, we are getting closer to this goal year after year.

There are three types of poliovirus, and infection or immunization with one type does not protect against another. Poliovirus type 1 has continued to cause outbreaks, but transmission by types 2 and 3 has been successfully interrupted by vaccination.

Poliovirus is transmitted through respiratory droplets but can also be transmitted through food or water that has come in contact with the feces of a person who has the virus.

It can survive for many days at normal temperatures. The last remaining outbreaks have been linked to areas with poor sanitation that are difficult to reach with vaccines. Afghanistan and Pakistan are the only two countries where wild polio is still endemic and are targeted by eradication programs to stop the virus from spreading to other countries.

Crucial role of vaccines

Vaccines play a critical role in eliminating polio. Fewer than 700 cases were reported worldwide in 2021.

In the UK, the injected polio vaccine is used. It contains inactivated virus (IPV) and will safely and effectively protect the immunized person from paralysis, but is less effective at inducing local immunity in the gut, so vaccinated persons can still become infected and shed infectious viruses, although they may not case is self showing symptoms.

IPV provides excellent protection for individuals, but is insufficient to contain an epidemic in poor sanitation conditions. The oral polio vaccine (OPV), which contains live but weakened virus, is ideal for this purpose. OPV is delivered by drip and requires no trained staff or sterile equipment to administer, allowing it to reach more communities.

This vaccine can induce strong intestinal immunity and prevent wild poliovirus shedding. Because it contains live virus, it can spread to and protect close contacts of the immunized person as well. It’s also cheaper than IPV.

The disadvantage of using OPV is that the weakened virus can mutate and, in rare cases, revert to paralysis-causing variants.

OPV is cleared by our immune system within days, but this may not be the case in immunocompromised people who may carry the virus longer, increasing the likelihood of mutations. In underimmunized countries, this can result in vaccine-derived poliovirus (VDPV) circulating. In fact, the virus found in London sewage was of the vaccine-derived strain VDPV type 2. There is still no wild poliovirus in the UK.

Vaccine-derived polio can cause asymptomatic infection in IPV vaccinated individuals and is excreted in the faeces since there is no local intestinal protection in IPV. It can therefore be detected in the wastewater.

Detection methods are sensitive, but a single positive reading would not trigger an alarm. Type 1 VDPV was recently detected in Kolkata sewage. It is believed to be an imported case of a vaccinated person with a weakened immune system who was unable to clear the vaccine strain from their body.

There are no reports of polio-related paralysis in the UK.

To prevent illness, we need to ensure family members are up to date with their vaccinations, especially children who may have missed a vaccination series due to the COVID pandemic. IPV is safe, free and effective in preventing polio. Unlike monkeypox vaccines, which are scarce and available to high-risk groups, IPV is readily available to anyone in the UK through their GP.

(Author: Zania Stamataki, Lecturer in Viral Immunology, University of Birmingham)

(Disclosure Statement: dr Zania Stamataki receives funding from the Medical Research Foundation, Innovate UK and BCHRF and she shares a PhD student with AstraZeneca on an iCASE MRC UKRI study.)

This article was republished by The Conversation under a Creative Commons license. Read the original article.

(Except for the headline, this story was not edited by NDTV staff and was published by a syndicated feed.)