British health officials have declared a national outbreak in London after finding evidence of a local outbreak of the polio virus.
Although health authorities have indicated that the term “national incident” has been used to describe the scale of the problem, no cases of polio have been identified and the risk to the community is low. However, health authorities have urged those who have not been fully vaccinated against the polio virus, especially children, to seek immediate vaccine.
“Most people in the UK are protected from childhood vaccinations, but in some communities with low vaccine coverage, people may be at risk,” said Dr. Vanessa Saliba, an epidemiologist with the UK Health 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 widespread in Britain and up to 8,000 cases of polio were reported each year.
Routine wastewater surveillance in the country infects polio once or twice a year, but from February to May, officials identified the virus in several samples collected in London. Shahin Huseynov is a technician with the World Health Organization’s European Vaccine Prevention and Immunization Program.
Genetic analysis shows that the samples have a common origin, probably from a person who traveled to the country around the New Year, Dr. Huseynov said. The last four samples collected seem to have evolved from this initial introduction in unvaccinated children.
“The importance of this result is that it is still important to ensure that all children have access to vaccines, even in well-developed countries, where vaccination coverage is still much higher than usual,” he said.
British officials are now collecting additional samples to try to identify the source of the virus. However, the sewage treatment plant, which identifies the samples, covers about 4 million people, almost half of the city, making it difficult to pinpoint the source.
Polio is most often spread from person to person who does not wash their hands properly and then touches food or water that someone else has swallowed. The virus grows in the gut and appears in the feces of infected people. In up to 1 percent of patients, the virus can damage the spine and cause paralysis.
“Most of the diseases are asymptomatic, and only one in 500 of these children is paralyzed,” he said. Dr. David Heymann, an infectious disease expert at the London School of Hygiene and Tropical Medicine, has previously led the WHO’s polio eradication program.
In Britain, polio vaccination is carried out with injectable poliovirus, which cannot be excreted in the feces. However, some countries around the world rely on a polio vaccine that contains a live, attenuated version of the virus. Immunized people can pass the virus in their feces for a short time and then turn it into sewage.
Health officials believe this is the case. The virus in the collected samples originated from a type of oral polio vaccine that is used to treat epidemics, the doctor said. Huseynov.
In recent months, the vaccine has been used only in Afghanistan, Pakistan and some countries in the Middle East and Africa, he said.
Wild polio has been eradicated in all countries of the world except Afghanistan and Pakistan. However, polio vaccine continues to cause small epidemics, especially in low-vaccination communities.
“Polio is endemic in the poorest parts of the world. Until it is eradicated around the world, the threat of importation and spread will continue in the UK and elsewhere, ”said Nicholas Grassley, a vaccine epidemiologist at Imperial College London.
The analysis suggests that the community is likely to be infected with young children. A person with a weakened immune system can carry the virus for months.
“The big question here is whether he is constantly circulating in the UK or whether he is an immunocompromised person,” the doctor said. Walter Orenstein, Deputy Director of the Emory Vaccine Center and former Director of the United States Immunization Program.
If this is the latter, Orenstein said, “they need to find someone who is immune-deficient.”