UK health authorities have declared a national incident after finding evidence suggesting local spread of poliovirus in London.
Although health authorities indicated that the term “national incident” was used to define 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 polio, especially young children, to seek vaccines immediately.
“Most of the UK population will be protected from childhood vaccinations, but in some communities with low vaccination coverage, people may remain at risk,” the doctor said. Vanessa Saliba, consultant epidemiologist at the UK Health Security Agency.
The last case of polio in the UK was in 1984 and the country was declared polio free in 2003. Before the introduction of the polio vaccine, epidemics were common in the UK, with up to 8,000 cases of paralysis reported annually.
Routine wastewater surveillance in the country detects poliovirus once or twice a year, but between February and May, officials identified the virus in several samples collected in London, according to Dr. B. Shahin Huseynov, World Organization Program Technician on vaccine-preventable diseases and immunization in Europe.
Genetic analysis suggests that the samples have a common origin, most likely a person who came to the country for the New Year. Huseynov said. The last four specimens collected appear to have originated from this initial introduction, probably from unvaccinated children.
“The importance of this finding is that even in well-developed countries where routine vaccination coverage is quite high, it is still important to ensure access to vaccines for all children,” he said.
British officials are now collecting additional samples and trying to determine the source of the virus. But the sewage treatment plant where the samples were found covers about 4 million people, nearly half the city, making it difficult to pinpoint the source.
Polio is most often transmitted by an infected person who does not wash their hands properly and then touches food or water swallowed by someone else. The virus thrives in the gut and appears in the feces of infected people. In 1% of patients, the virus can infect the spine and cause paralysis.
“Most of the disease is asymptomatic, only one in 500 children is actually paralyzed,” he said. Dr. David Heymann is an infectious disease expert at the London School of Hygiene and Tropical Medicine and previously led the WHO polio eradication programme.
In the UK, polio immunization is given with inactivated poliovirus, which cannot be excreted in the faeces. But some parts of the world rely on an oral polio vaccine containing a live, attenuated version of the virus. Immunized people can shed this virus for a short time in their faeces, which can then end up in sewage.
This, according to health officials, is exactly what happened in this case. The virus in the samples collected was derived from an oral polio vaccine that is used to contain outbreaks. Huseynov.
This type of vaccine has only been used in Afghanistan, Pakistan and some countries in the Middle East and Africa in recent months, he said.
Wild poliovirus has been eradicated from 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 eradicated globally, the risk of importation and spread in the UK and elsewhere will remain,” said Nicholas Grassley, a vaccine epidemiologist at Imperial College London.
Analysis so far suggests community transmission of the virus, most likely among young children. A less likely possibility is that one immunocompromised person shed the virus for several months.
“The big issue here is whether it’s constantly circulating in the UK or if it’s an immunocompromised person,” the doctor said. Walter Orenstein, associate director of the Emory Vaccine Center and former director of the US Immunization Program.
If it’s the latter, Orenstein said, “they need to find someone with an immunodeficiency.”