Britain declares national incident after polio virus found in London

British health authorities have declared a national incident after finding evidence suggesting local spread of poliovirus in London.

No cases of poliomyelitis have been identified so far and the risk to the public is low. But health authorities have urged anyone who is not fully immune to poliovirus, especially young children, to get vaccinated immediately.

“Most of the UK population will be protected from childhood vaccination, but in some communities with low vaccination coverage individuals may remain at risk,” said Dr Vanessa Saliba, consultant epidemiologist for the UK Safety Agency. sanitary.

The last case of polio in Britain was in 1984 and the country was declared polio-free in 2003. Before the introduction of the polio vaccine, outbreaks were common in Britain, with up to 8,000 cases of paralysis reported each year.

Routine sewage monitoring in the country detects poliovirus once or twice a year, but between February and May officials identified the virus in several samples taken in London, according to Dr Shahin Huseynov, technical officer of the World Health Organization. disease control and vaccination program in Europe.

Genetic analysis suggests the samples have a common origin, most likely an individual who traveled to the country around New Years, Dr Huseynov said. The last four samples collected seem to have evolved since this initial introduction, probably in unvaccinated children.

“The significance of this finding is that even in well-developed countries, countries where routine vaccination coverage is quite high, it is still important to ensure that all children have access to vaccines,” he said. declared.

British authorities are now collecting additional samples and trying to identify the source of the virus. But the sewage treatment plant that identified the samples covers about 4 million people, nearly half of the city, making it difficult to identify the source.

Polio is most often spread by an infected person not washing their hands properly and then touching food or water someone else has eaten. The virus grows in the intestine and emerges in the feces of infected people. In up to 1% of patients, the virus can infect the spine and cause paralysis.

“Most of the disease is asymptomatic, only about one in 500 children is actually paralyzed,” said Dr David Heymann, an infectious disease expert at the London School of Hygiene and Tropical Medicine, who previously led the WHO’s polio eradication programme.

In Britain, vaccination against poliomyelitis is carried out with an injected inactivated poliovirus, which cannot be excreted through faeces. But some countries around the world rely on an oral polio vaccine that contains a live, weakened version of the virus. Immune people can briefly shed this virus in their faeces, which can then end up in sewage.

That’s what health officials believe happened in this case. The virus in the collected samples came from a type of oral polio vaccine used to contain outbreaks, according to Dr Huseynov.

In recent months, this type of vaccine has only been used in Afghanistan, Pakistan and some countries in the Middle East and Africa, he said.

Wild poliovirus has been eliminated from every country in the world except Afghanistan and Pakistan. But vaccine-derived polio continues to cause small outbreaks, especially in communities with low vaccination coverage.

“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,” said Nicholas Grassly, vaccine epidemiologist at Imperial College London.

Analysis so far suggests community transmission, most likely among young children. A less likely possibility is that a single immunocompromised individual shed virus for months.

“The big issue here is whether he is permanently circulating in the UK or whether he is an immunocompromised person,” said Dr Walter Orenstein, associate director of the Emory Vaccine Center and former director of the program. vaccination in the United States.

If it’s the latter, Orenstein said, “they have to find that immunocompromised person.”

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