UK health officials have concluded that there has been human-to-human transmission of the poliovirus in certain areas of London in recent months. The disease was eradicated in the UK in 2003, so the signs found have alerted the Health Safety Authority (UKHSA) enough to declare it a ‘national incident’. This is the step before a declaration of emergency and requires a detailed investigation of the alarm.
Between February and May of this year, several genetically very similar samples of the virus were detected at the Beckton sewage treatment plant east of the British capital. The plant supplies more than four million inhabitants.
Up until just over a decade ago, the UK provided the oral polio vaccine, which contained a ‘weakened’ version of the virus capable of stimulating the immune system. This type of vaccine is already used in a limited number of countries. In the West, vaccination against polio is now done with “inactivated vaccines” that contain a dose of the pathogen that has already been killed. They need booster injections to effectively stimulate the defenses, but they avoid the risk of the virus mutating and becoming deadly.
It is normal for routine inspections every year to find some samples of the oral vaccine virus in UK sewage, which is still very present during campaigns in countries like Pakistan, Afghanistan or Nigeria. The conclusion is always that it came from someone who brought the virus to the UK. The seriousness of the recent discovery lies in the fact that the samples detected correspond, similarly and continuously over a period of time, to a type 2 poliovirus (VDPV2), a “vaccine-derived” mutation that can cause serious illnesses such as paralysis , in people who are not vaccinated.
“Vaccine-derived poliovirus is extremely rare and the public health risk remains extremely low,” said Dr. Vanessa Saliba, Epidemiology Advisor to the UKHSA. “However, they can spread, particularly in communities where immunization coverage is low,” said Saliba, who has urged parents whose children do not have their immunological records up to date to see a pediatrician immediately. The vaccine comes as a three-dose cycle. Before you turn a year old; at three; and finally at fourteen. While 92% of minors across the UK have completed their vaccination, in London the figure is 86%. Although the World Health Organization considers the UK to be a polio eradicated country with a very low risk of transmission due to high vaccination levels, vaccination coverage has gradually slowed.
“Most Londoners are protected from polio and don’t need to take any exceptional measures,” said Jane Clegg, the NHS’s chief nurse in London. “But the NHS will start contacting parents of children under five who don’t have their cards up to date to encourage them to do so,” Clegg said.
So far, the health authorities have not treated any patient with symptoms of the disease. Polio is usually transmitted by people who have not washed their hands after defecation and who touch food or water consumed by others. In rare cases, transmission can occur through coughing or sneezing. Most infected people do not develop any symptoms or simply suffer from a flu-like illness for two or three weeks. But in some rare cases (one in a hundred to one in a thousand) the virus can attack nerves in the spine or base of the brain and cause paralysis, usually in the legs. When it affects the muscles that control the respiratory system, the consequences can be deadly.
UK health authorities have extended the investigation to areas bordering the sewage treatment plant where the samples were found and have placed health workers on alert to monitor the possible emergence of a symptomatic patient.