LONDON — Every child in London aged 1 to 9 should be offered a booster dose of the polio vaccine, Britain’s health officials said on Wednesday after traces of the virus turned up in sewage samples in a quarter of the boroughs but no isolated cases of the disease were found reported.
Health officials declared a national incident in June – a term used to underscore the potential seriousness of the problem – after sewage samples suggested the virus was spreading in London. Now, officials said, samples showed it had spread beyond a tight network of a few people.
Normally, routine sewage monitoring in the UK picks up the virus once or twice a year, the UK Health Security Agency said in a statement, but between February and July 116 samples of the type 2 poliovirus were detected in samples from eight London boroughs north and east of town.
“No cases of polio have been reported and the risk is low for the majority of the population that is fully vaccinated,” said Dr. Vanessa Saliba, consultant epidemiologist at the health agency, in the statement.
“But we do know that areas of London where poliovirus is transmitted have some of the lowest vaccination rates. Because of this, the virus is spreading in these communities, putting those residents who are not fully vaccinated at greater risk.”
Polio, which can cause paralysis, was once a deeply feared childhood disease that vaccines have virtually eradicated. Britain’s last known case was in 1984, and a case discovered in Rockland County, NY last month was the first in the United States in almost a decade. Wild poliovirus has been eliminated in every country in the world except Afghanistan and Pakistan.
The traces found in London’s sewage were, as in the case in New York State, of poliovirus derived from the oral polio vaccine, which uses a weakened live form of the virus that immunized people shed for a short time.
In rare cases, the virus can spread in communities with low immunization coverage. In very rare cases – generally when the vaccine’s protection is so low that it has been circulating for at least a year, according to the World Health Organization – it can gradually mutate back into a form that can be crippling.
Most of London’s sewage samples contained a form of the virus that’s still very close to the harmless version in the vaccine, Britain’s health safety agency said, but a few carried enough mutations to cause serious illness.
Oral polio vaccine is no longer routinely given in Britain, which, like the United States, now prefers a vaccine that uses inactivated — virtually dead — viruses.
The UK Health Security Agency said child vaccination uptake was lower in London than the rest of the country. Recent figures from London suggest a broader immunization coverage of 86.6 percent, according to the Global Polio Eradication Initiative, which should generally be enough to prevent widespread transmission of the virus.
“While the majority of Londoners are protected from polio, the NHS will shortly be contacting parents of eligible children aged one to nine to offer them a booster dose to ensure they have maximum protection from the virus,” said Jane Clegg. the senior nurse at Britain’s National Health Service in London, adding that medics were already reaching out to parents and carers of children whose vaccinations were not up to date.
Britain’s Health Security Agency said on Wednesday it was working closely with the World Health Organization and health authorities in New York and Israel to investigate the links between the poliovirus outbreak in London and recent episodes in Israel and the United States.
Many countries around the world, including the United States and Israel, already offer an additional polio booster shot as part of their childhood immunization schedule. The UK routinely provides a pre-school booster vaccine containing polio to children aged 3 years and 4 months.
Britain’s health agency also said on Wednesday that it had already stepped up sewage monitoring across London and that 10 to 15 sites across the country would do so be examined to see if the polio virus has spread outside of London.