Britain’s health authorities have announced a national outbreak of poliovirus in London after it suggested a local outbreak.
So far no cases of polio have been identified and the risk to the public is low. But health authorities have called for immediate immunization of anyone, especially young children, who have not been fully vaccinated against the polio virus.
“The majority of the UK population will be protected from childhood immunizations, but people from certain communities with low vaccine coverage may be at risk,” said Dr Vanessa Saliba, a consultant epidemiologist at the UK Health Security Agency.
The last case of polio in Britain was in 1984, and the country was declared polio free in 2003. Prior to the introduction of the polio vaccine, epidemics were common in Britain, with up to 8,000 cases of paralysis occurring each year.
According to Dr. Shahin Husseinov, the World Health Organization’s vaccine-preventable technician, routine surveillance of the country’s sewage system detects the virus once or twice a year, but between February and May, officials identified the virus in several samples collected in London. Disease and Immunization Program in Europe.
From the genetic analysis it is known that the samples have a common source, probably a person who traveled to the country around the new year, Dr. Husseinov said. The last four samples collected appear to have originated from this early identification, probably in immunized children.
“The importance of this research is that even in developed countries, in countries where vaccination coverage is generally high, it is important to ensure that all children still have access to the vaccine,” he said.
British officials are now collecting additional samples and trying to identify the source of the virus. But the samples identified by the wastewater treatment plant, which covers about 4 million people, about half the city, make it challenging to identify the source.
Polio is often spread by an infected person who does not wash their hands properly and then touches food or water eaten by someone else. The virus spreads to the intestines and is excreted 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 actually paralyzed,” he said. Dr David Heyman, an infectious disease specialist at the London School of Hygiene and Tropical Medicine who previously led the WHO’s polio eradication program.
In Britain, immunization for polio is carried out by an injectable inactivated poliovirus, which cannot be excreted in the feces. But some countries in the world rely on the oral polio vaccine to provide a live, weakened version of the virus. Immunized people can briefly pass the virus into their feces, which can later turn into sewers.
That is what the health officials think. According to Dr. Husseinov, the virus in the collected samples came from a type of oral polio vaccine used to contain the outbreak.
In recent months, such vaccines have only been used in Afghanistan, Pakistan and some countries in the Middle East and Africa, he said.
The wild poliovirus has been eradicated from every country in the world except Afghanistan and Pakistan. But vaccine-derived polio continues to cause minor outbreaks, especially in communities with low immunization coverage.
“Polio survives in the poorest part of the world. Until it is eliminated worldwide, the risk of importing and spreading to the UK and elsewhere will continue, “said Nicholas Grassley, a vaccine epidemiologist at Imperial College London.
So far the analysis has said community transmission, probably in young children. There is a low probability that a single immunocompromised person has spread the virus for several months.
Dr. Walter Ornstein, associate director of the Emory Vaccine Center and former director of the U.S. Immunization Program, said: “The big issue here is whether it is constantly being promoted in the UK or whether it is an immunodeficiency person.”
If this were the case then, Orinstein said, “they need to find that immunodeficient person.”