Announcing a ‘national incident’ yesterday after the poliovirus was found in London’s sewers, public health officials in the UK asked doctors to be on the lookout for polio cases and urged residents to check that they are up to date with their vaccinations for now. disease. The source of the virus is still a mystery, but it is probably someone outside the UK who recently received the oral polio vaccine (OPV), which uses a live but attenuated virus and is no longer used in the UK.
Most polio infections are asymptomatic and no cases have been reported in the United Kingdom. But with vaccination rates below 90% in some communities in London, there are fears that it will not continue. The emergence of poliovirus in London is a reminder, “that no country is immune to re-infection with polio or its re-emergence until the disease is eradicated everywhere,” said Oliver Rosenbauer, spokesman for the Global Polio Eradication Initiative. . .
Polio has been eliminated in much of the world, but the virus is still endemic in Afghanistan and Pakistan, and another 30 countries in Africa, Europe and the Middle East have already been identified as “outbreak countries” where the virus has recently spread. The spread is planted either by the wild-type virus, which continues to exist in Afghanistan or Pakistan, or by the OPV virus, which has regained its ability to cause disease in unvaccinated people.
In the United Kingdom, the virus was found in samples taken between February and June by Beckton Sewage Treatment Works, which treats wastewater from 4 million people in north and east London. It did not cause alarm at first; wastewater monitoring programs in the UK typically detect several such samples each year, discarded by recent arrivals who have received OPV.
Such traces of sewage usually disappear again quite quickly. This time, the virus continued to appear in London for several months, and several closely related versions of the virus have been found in recent samples. Genetic changes suggest that the virus continues to grow, a sign that it may spread to a small number of people.
Joseph Swan, the WHO’s polio communications officer, says it is more likely to be more widespread, given the generally high coverage of vaccines in the UK, which, like most rich countries, uses multiple doses of a killed virus vaccine. And he emphasizes that there is still no direct evidence that the virus is spread from person to person. But staff encourage people to check that they and their children have received all the recommended doses of vaccine.
The detection of polio in London is the second this year in a place where there is usually no virus. On March 7, an unvaccinated 3-year-old child in Israel who developed paralysis was diagnosed with polio, and the country has found polio in 25 sewer samples so far this year, mostly in or near Jerusalem. The virus there is also a vaccine-derived strain, but it is a type 3 strain that is not related to the type 2 virus found in London. Rapid detection in both Israel and the United Kingdom shows that polio surveillance systems are working there, Rosenbauer said.
Israel and the Palestinian National Authority have stepped up their efforts to vaccinate in response, and the virus has not been found in sewers there since March. But COVID-19 has made the job harder, says Itamar Grotto, an epidemiologist on infectious diseases at Ben-Gurion University in the Negev. Both public and public health personnel are exhausted after the pandemic and the many COVID-19 vaccination campaigns, he said, and in some groups, hesitation about vaccines has increased.
Officials in London are now taking sewage samples upstream from the Beckton treatment plant to see if they can narrow the source of the virus and perhaps focus more specifically on vaccination campaigns.
OPV, which brought the virus to both the United Kingdom and Israel, has advantages in the regions where the poliovirus spreads. Not only is it inexpensive and easy to administer, but the live virus in the vaccine can still replicate in the recipient, triggering a strong immune defense in the gut that can stop further transmission of the virus, helping to strengthen the defense of the virus. community against future outbreaks. And although it has evolved from time to time to regain its virulence, healthcare professionals are beginning to introduce a more stable form of OPV, which they hope will reduce the risk of these reversals.
Rosenbauer, meanwhile, says: “The main thing states can do … is ensure strong disease surveillance and a high range of vaccinations to minimize the risk and consequences of recurrence.”