UK health authorities have declared a national incident after finding evidence suggesting the local spread of the poliovirus in London.
Although health authorities indicated that the use of the term “national incident” was used to describe the extent of the problem, no cases of polio have been identified so far and the risk to the population is low. But health authorities have urged anyone who is not fully vaccinated against poliovirus, especially young children, to seek vaccines immediately.
“The majority of the UK population will be protected from childhood vaccination, but in some communities with low vaccine coverage, people may remain at risk,” said Dr Vanessa Saliba, the Agency’s consultant epidemiologist. of the United Kingdom.
The last case of poliomyelitis in Britain was in 1984, and the country was declared free of poliomyelitis in 2003. Prior to the introduction of the polio vaccine, epidemics were common in Britain, with up to 8,000 cases of paralysis each year.
Routine wastewater monitoring in the country detects the poliovirus once or twice a year, but between February and May, officials identified the virus in several samples collected in London, according to Dr. Shahin Huseynov, technical officer of the World Health Organization that can be prevented by vaccine. immunization and disease program in Europe.
Genetic analysis suggests the samples have a common origin, probably an individual who traveled to the country during the New Year, Dr. Huseynov said. 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 regular vaccination coverage is quite high, it is still important to ensure that all children have access to vaccines,” he said.
British officials are collecting additional samples and are trying to identify the source of the virus. But the wastewater treatment plant that identified the samples covers about 4 million people, nearly half of the city, making it difficult to identify the source.
Poliomyelitis is most often transmitted by an infected person who does not wash their hands properly and then touches food or water ingested by another person. The virus develops in the gut and emerges in the feces of infected people. In up to 1 percent of patients, the virus can infect the spine and cause paralysis.
“Most of the disease is asymptomatic, only one in 500 children is paralyzed,” he said. Dr. David Heymann, an infectious disease expert at the London School of Hygiene and Tropical Medicine who previously led the WHO polio eradication program.
In Britain, polio immunization is carried out with an inactivated poliovirus injected, which cannot be excreted in the feces. But some countries in the world depend on an oral polio vaccine that contains a living and weakened version of the virus. Vaccinated people can briefly remove this virus in their feces, which can then appear in the sewage.
This is what health officials believe happened in this case. The virus in the samples collected came from a type of oral polio vaccine that is used to contain outbreaks, according to Dr. Huseynov.
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 wiped out in every country in the world except Afghanistan and Pakistan. But vaccine-derived poliomyelitis continues to cause small outbreaks, especially in communities with low vaccination coverage.
“Poliomyelitis persists in some of the poorest parts of the world. Until it is eradicated worldwide, the risk of importation and spread to the UK and elsewhere will continue,” said Nicholas Grassly, a vaccine epidemiologist at Imperial College London.
The analysis so far suggests community transmission, most likely among young children. A less likely chance is that a single immunocompromised individual will have eliminated the virus for months.
“The big issue here is whether he’s been circulating continuously in the UK or if he’s an immunodeficient person,” said Dr. Walter Orenstein, associate director of the Emory Vaccine Center and former director of the U.S. Immunization Program. .
If it’s the latter, Orenstein said, “they should find that person immunodeficient.”