Health authorities in the UK have announced a national incident after finding evidence suggesting the local spread of poliovirus in London.
Although health authorities have indicated that the use of the term “national incident” has been used to delineate the scope of the problem, no cases of polio have been identified so far and the risk to the public is low. But health officials have urged anyone who is not fully immune to the poliovirus, especially young children, to seek vaccines immediately.
“Most of the UK population will be protected from childhood vaccinations, but in some low-vaccine communities people may remain at risk,” said Dr Vanessa Saliba, a consultant epidemiologist with the Health Security Agency. of the United Kingdom.
The last case of polio in the UK was in 1984, and the country was declared polio-free in 2003. Prior to the introduction of the polio vaccine, epidemics were common in the UK, with up to 8,000 cases of paralysis reported each year.
Routine sewage monitoring in the country catches the poliovirus once or twice a year, but between February and May, officers identified the virus in several samples collected in London, according to Dr. Shahin Husseinov, a technical officer with the World Health Organization. immunization program in Europe.
Genetic analysis shows that the samples are of common origin, most likely a person traveled to the country around New Year, said Dr. Husseinov. The last four samples collected appear to have evolved from this initial introduction, probably in unvaccinated children.
“The importance of this finding is that even in well-developed countries, countries where the usual coverage of vaccines is quite high, it is still important to ensure that all children have access to vaccines,” he said.
British officials are now collecting additional samples and trying to identify the source of the virus. But the sewage treatment plant that identifies the samples covers about 4 million people, almost half of the city, which makes it a challenge to determine the source.
Polio is most commonly spread by an infected person who does not wash their hands well and then touches food or water ingested by someone else. The virus thrives in the gut and appears 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, it’s only about one in 500 children who are actually paralyzed,” he said. Dr. David Hayman, an infectious disease expert at the London School of Hygiene and Tropical Medicine, previously led the WHO’s polio eradication program.
In the UK, polio immunization is given with injected inactivated poliovirus that cannot be excreted in the faeces. But some countries around the world are relying on an oral polio vaccine that contains a live, attenuated version of the virus. Immunized people can briefly excrete this virus in their feces, which can then end up in the sewer.
This is the opinion of the health officials in this case. The virus in the collected samples comes from an oral polio vaccine that is used to limit outbreaks, according to Dr. Husseinov.
In recent months, this type of vaccine has been used only in Afghanistan, Pakistan and some countries in the Middle East and Africa, he said.
Wild poliovirus has been eliminated in all countries of 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 destroyed worldwide, the risk of importation and distribution in the UK and elsewhere will continue, “said Nicholas Grassley, a vaccine epidemiologist at Imperial College London.
The analysis so far suggests transmission in the community, most likely among young children. It is less likely that a single immunocompromised individual has shed the virus within months.
“The big problem here is whether he’s constantly circulating in the UK or an immunodeficient person,” said Dr. Walter Orenstein, associate director of the Emory Vaccine Center and former director of the United States Immunization Program.
If the latter, Orenstein said, “they have to find this immunodeficient person.”