UK confirms first vaccine-derived poliovirus in 38 years
•Labels situation national incident, urges immunisation as WHO preaches surveillance
Global Polio Laboratory Network (GPLN) of the World Health Organisation (WHO) and British health authorities have confirmed first vaccine-derived poliovirus in London, United Kingdom since 1984.
Consequently, Britain, yesterday, declared the situation as National Incident after finding evidence suggesting local spread of poliovirus in London, even as it urged those who were not fully immunised to seek vaccines immediately.
WHO, also, charged nations to strengthen surveillance for rapid detection of new virus importation and enhanced response.
The global agency, in a statement, said isolation of type two vaccine-derived poliovirus (VDPV2) from environmental samples in London was detected as part of ongoing disease surveillance.
Britain was declared polio-free in 2003. Before the introduction of the polio vaccine, epidemics were prevalent, with up to 8,000 cases of paralysis reported yearly.
WHO, yesterday, said it was important to note that the virus had been isolated from environmental samples only, as no associated cases of paralysis have been detected. Recent coverage for the primary course of DTaP/IPV/Hib/HepB vaccination, which protects against several diseases, including polio in London, suggests immunisation coverage of 86.6 per cent.
Wild poliovirus has been eliminated from every country of the world, except Afghanistan and Pakistan. But vaccine-derived polio continues to cause small outbreaks, particularly in communities with low vaccination coverage.
An infected person, who does not properly wash his or her hands and then touches food or water ingested by someone else, spreads the virus most often. The disease thrives in the gut and emerges in the feces of infected people. In up to one per cent of patients, the ailment can infect the spine and cause paralysis.
According to The New York Times, although health authorities indicated that the use of the term “national incident” was used to outline the scope of the issue, no cases of polio have been identified so far, and the risk to the public is low. But health authorities urged anyone who is not fully immunised against poliovirus, particularly young children, to immediately seek vaccines.
A consultant epidemiologist for the UK Health Security Agency, Dr. Vanessa Saliba, said: “Most of the UK population will be protected from vaccination in childhood, but in some communities with low vaccine coverage, individuals may remain at risk.”
To the technical officer for WHO’s vaccine-preventable diseases and immunisation programme in Europe, Dr. Shahin Huseynov, routine surveillance of sewage in the country picks up poliovirus once or twice a year, but between February and May, officials identified the virus in several samples collected in London.
Huseynov said genetic analysis suggests that the samples have a common origin, most likely an individual, who traveled to the country around the New Year. The last four samples appear to have evolved from this initial introduction, likely in unvaccinated children.
British officials are now collecting additional samples and trying to identify the source of the virus. But the wastewater treatment plant that identified the samples covers about four million people, almost half of the city, making it challenging to pinpoint the source.
An infectious disease expert at the London School of Hygiene and Tropical Medicine, who previously led the WHO’s polio eradication programme, Dr. David Heymann, observed: “Most of the disease is asymptomatic, it is only about one in 500 children who are actually paralysed.”
In Britain, immunisation for polio is carried out with an injected inactivated poliovirus, which cannot be shed through feces. But some countries of the world rely on an oral polio vaccine that contains a live, weakened version of the virus. Immunised people can briefly shed this virus in their feces, which can then turn up in sewage.
Huseynov said that was what health officials believe happened in this case. The virus in the collected samples came from a type of oral polio vaccine that was used to contain outbreaks.
He said, in recent months, that type of vaccine had been used only in Afghanistan, Pakistan and some countries in the Middle East and Africa.
A vaccine epidemiologist at Imperial College London, Nicholas Grassly, submitted: “Polio persists in some of the poorest parts of the world. Until it is eradicated worldwide, the risk of importation and spread in the UK and elsewhere will continue.”