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expert reaction to report from the UKHSA of poliovirus detected in sewage from North and East London

The UK Health Security Agency (UKHSA) have announced that an investigation is underway following poliovirus detection in sewage from North and East London.


Dr Philip Minor, retired freelance consultant, formerly of the National Institute for Biological Standards and Control (was Head of the Division of Virology there until retirement in 2017), said:

“A type 2 poliovirus related to the strain found in the oral polio vaccine has been detected in sewage samples from the Becton sewage works in North London.  The samples were taken from February to June this year, which is a prolonged period and they have not been hard to find – it is difficult to put a figure on it but this suggests there is more of it present than if you just had one person.  The isolates are very similar but show signs of a gradual drift in sequence over time which suggests that they come from a chronically infected individual or more likely infections circulating in a sub-population with poor immunity.  While viruses have been detected in sewage in the past they have been one offs probably from someone who picked up the virus on a visit abroad.  To my knowledge this is the first sign of on-going circulation in the UK since OPV usage stopped.

“Poliovirus is a picornavirus (‘pico: small-rna virus’), a family that have characteristics in common such as an RNA genome and a non-enveloped capsid.  It includes sub-groups such as the enteroviruses that include poliovirus which has a genome of about 7500 nucleotides.  The viruses sampled have the characteristics of circulating vaccine derived polioviruses (cVDPV), in that they are recombinants with another unidentified human enterovirus, although they may not have drifted in sequence sufficiently to fit all the criteria yet.  Almost all of the cVDPVs that have been previously described have been recombinants between the OPV vaccine strain (most often type 2) and some other enterovirus, presumed to be some unidentified group C entero virus.  That these viruses are recombinants is a totally natural phenomenon and not anything sinister.  Such viruses are currently fairly common in Africa and in polio endemic countries such as Afghanistan and Pakistan.  They can cause poliomyelitis.  That the Becton viruses are recombinants is evidence to me that they come from a cVDPV, and I think the most likely source is outside the UK.

“Most of the population is not at risk because hygiene standards and immunity are both high.  The observation is a cause for concern but not panic.  However the easiest explanation for it is that there is a community of susceptible individuals who are at risk, probably because of poor vaccine uptake, and they are a cause for real concern.  I believe there are ongoing attempts to identify them and try and immunise them, the best way to deal with the issue.  Pockets of poor vaccine uptake are known in London.

“Sewage surveillance is cheap.  It does not depend on finding cases or mass surveillance (as used extensively for covid for instance, where sewage surveillance also plays a part).  Using modern sequencing technology it is possible to look for any virus that may be shed in the faeces in sufficient amounts.  There are a lot of virus types that fall into this category.  With the power of modern sequencing methods you do not even need to know what you are looking for.  In my opinion there should be major ongoing investment in sewage surveillance in preparing for pandemics.”


Prof Beate Kampmann, Professor of Paediatric Infection & Immunity; and Director of The Vaccine Centre, London School of Hygiene and Tropical Medicine, said:

“More than 20 countries in the world have reported circulating vaccine-derived polio virus (cVDPV), and the main worry here is the genetic connectedness of the strains found in the sewage water in North London, as it shows transmission in a group and not just a single “excreter”.  These cVDPV can develop from individuals who received oral polio virus vaccine in a different country that continues to use oral polio vaccine, continue to excrete polio virus and can pass it on over long times.  In the UK we have not been using oral polio vaccine since 2003, given that polio was eradicated in the UK.  Here we use the inactivated vaccine which does not carry the risk of VDPV, but also does not induce immunity at the level of the gut mucosa-which is the advantage of the oral vaccine.  The trade-off is that the attenuated live virus used in the oral polio vaccine can mutate – and this then leads to VDPV.  Although to date no cases of vaccine-associated paralysis have resulted from this finding, we must not be complacent, and it reminds us all how vital the comprehensive use of vaccines against polio is.  Some people might be confused by the fact that a vaccine can be used to combat a vaccine-derived strain of polio, as this appears counter-intuitive at first.  However, multiplication of vaccine-derived polio viruses can only happen if there is poor immunity against polio in the community, and with polio vaccine coverage at only 86% in London we have a potential pool of susceptibles.  Hence the mission now has to be that everyone looks at their immunisation books and gets their series completed, so we close the gap and don’t allow these strains to spread.

“A novel type of oral polio vaccine called nOPV has also been developed, it is designed not to allow for these mutations, and is already being used in emergencies to control outbreaks of VDPV in other parts of the world – this could be an option if we really do see wider spread.”


Prof David Salisbury, Associate Fellow, Programme for Global Health, Chatham House; and Chair, WHO Global Commission for Certification of Polio Eradication, said:

“It should not have come as a surprise that polio vaccine derived viruses have been found in sewage in London.  The original vaccine virus will have come from where oral polio vaccine type 2 has been used – parts of Africa, Afghanistan and Pakistan.  The most likely person to bring the virus would have been a child.  The genetic changes in the virus imply that it has circulated amongst individuals, including possibly those who have been vaccinated with inactivated polio vaccine (IPV) as has been used for almost twenty years in the U.K. immunisation programme.

“Fully vaccinated individuals (five doses) do not require further boosters.  Parents of children who have not completed their recommended doses of vaccine should contact their Primary Care provider.  This is especially important in London where these viruses have been identified and vaccine coverage is lower than elsewhere.

“This event should serve as a timely reminder for the U.K. that wild poliovirus type 1 has not been eradicated and therefore the risk of importation remains until Global Certification.  The risk of importation of vaccine derived polioviruses also will persist until the use of oral (live) polio viruses is phased out.  There is also a risk of loss of polioviruses from manufacturers or laboratories that work on or store the virus.

“High quality surveillance of polioviruses remains essential.  The Health Security Agency needs to provide information on how many U.K. environmental surveillance sites are testing for polioviruses, how frequently samples are taken and tested, and their results.  Without extensive national environmental poliovirus surveillance, it is not possible to know if this problem is more widespread.”


Prof Jonathan Ball, Professor of Molecular Virology, University of Nottingham, said:

“This finding really shows the value of sewage surveillance, which can be used to detect circulation of a variety of infections – including polio and SARS-Cov-2 – in the wider population.

“In the UK we use a killed vaccine so this vaccine strain of polio is likely to have been introduced from a country where the virus is actively circulating, which is where you would use live virus vaccines.

“The disease threat to the UK is low because we use the killed vaccine, which will protect from disease, but we might see some continued spread of the vaccine strain as killed vaccine doesn’t always protect from infection.  Ultimately though, this virus should disappear because of the high levels of vaccination here.”


Prof Ian Jones, Professor of Virology, University of Reading, said:

“The finding of poliovirus in sewage waters has been reported in many other parts of the world, often associated with the movement of people from areas of conflict.  It arises as some people can be chronically infected and shed virus constantly, or from someone who has been recently vaccinated with the live OPV (oral poliovirus vaccine).  It’s a surprise to find it here but the threat is low as the majority of the population is immune.  However, it serves as a reminder that infectious agents spread by all routes and that parental adherence to the vaccine card is important.”


Prof Paul Hunter, Professor in Medicine, UEA, said:

“Vaccine derived poliovirus is virus that evolved from the vaccine strain and is circulating in the community.  These links give a sound summary of these issues and

“There are two types of polio vaccine, attenuated and inactivated.  Attenuated vaccine still causes infection but doesn’t cause the paralysis except in very rare situations.  Inactivated vaccine as used in the UK doesn’t cause infection.  Given that the UK doesn’t use live polio vaccine this infection has probably been imported from a country where live vaccine is still being used.

“In populations with low vaccine uptake of it is possible that the live polio vaccine can spread from one person to another.  If this is sustained, over time (one or two years) this vaccine derived virus can mutate to become fully virulent again and can start to cause paralysis in people who have not been vaccinated.

“The positive results reported today have been detected is sewage/wastewater samples and not in humans.  There have not been any paralytic cases so far.  So at the moment there is unlikely to be any immediate risk to public health, but if such transmission continues then the risk is that the virus will eventually evolve into one that does cause paralysis.  If that does happen then this could pose a serious risk to people who have not been vaccinated.  This is the reason why the world is moving away from using live attenuated vaccines.

“Such vaccine derived transmission events are well described and most ultimately fizzle out without causing any harm but that depends on vaccination coverage being improved.”


Dr Kathleen O’Reilly, Associate Professor in Statistics for Infectious Disease and expert in Polio Eradication, said:

“In these investigations, ‘vaccine-derived’ poliovirus has been detected from several sewage samples from the north London area. These findings suggest that there may be localised spread of poliovirus, most likely within individuals that are not up to date with polio immunisations. The most effective way to prevent further spread is to check vaccination histories, especially of young children, to check that polio vaccination is included. The UK vaccinates against polio using the ‘inactivated’ vaccine (called the IPV) where there is no risk of onward spread. For families that have recently moved to the UK, I recommend that they contact their local doctors (“GP”) and they will provide further support to confirm that children are up to date with their vaccines. It is free to register.

“The findings are from sewage sampling, as people infected with poliovirus shed virus in their faeces, which can then be detected in sewage treatment plants. Sewage surveillance for polio, and other pathogens, have been extremely useful to detect emergence of pathogens and respond to these detections early, preventing disease and onward spread. The surveillance in London that identified vaccine-derived poliovirus is such an example. Another example is from Israel in 2014 where poliovirus was also detected in sewage samples, and polio cases were prevented through vaccination.

“Vaccine-derived poliovirus is present in many countries across the world, especially within the African continent and some countries in Asia. The origin of the vaccine-derived poliovirus is from certain versions of the live oral polio vaccine, which are used in a small number of countries. The UK has not used this vaccine for some years. Until all poliovirus are stopped globally, all countries are at risk, highlighting the need for polio eradication, and continued global support for such an endeavour.”


Prof Nicholas Grassly, Professor of Vaccine Epidemiology, Imperial College London, said:

What is vaccine-like and vaccine-derived poliovirus?  How/why can people who have had the oral polio vaccine shed virus; is the virus they shed normally a risk to other people?

“Oral polio vaccine contains a weakened, live virus that immunises us by growing in the intestine for a short period during which it can be detected in stool.  This virus can occasionally be transmitted and very rarely it can spread further to cause an outbreak of vaccine-derived poliovirus.  Whilst rare, these vaccine-derived polioviruses have lost their attenuating mutations and and are just as likely as the wild-type strain to cause paralysis.

Which polio vaccine do we currently use in the UK?  Why do some other countries still use (live) oral polio vaccine?

“Oral polio vaccine is easy to administer and gives good gut immunity that protects against infection and poliovirus shedding in stool if exposed.  It is needed to stop polio outbreaks in countries with poor sanitation where food and water may be contaminated with human waste.  In the UK the oral vaccine was replaced with an injectable inactivated polio vaccine in 2004.

Is it unusual to detect these viruses in sewage sampling?  What makes this situation different from previous situations?

“Polio persists in some of the poorest parts of the world and the UK quite frequently detects imported virus in sewage samples.  In this case, genetically related viruses have been detected since February in sewage from north and east London suggesting there may be local circulation.  Fortunately, so far no one has developed symptoms of the disease, which only affects about 1 in 200 of those infected, but it is important that children are fully up-to-date with their polio vaccines.  Until polio is eradicated globally we will continue to face this infectious disease threat.”


Dr David Elliman, consultant paediatrician at Great Ormond Street Hospital, said:

“Parents sometimes ask why, when diseases are uncommon in UK, or in the case of polio has been eliminated, do we continue to vaccinate against them.  The answer is that, although we are an island, we are not isolated from the rest of the world, which means diseases could be brought in from abroad.  The finding of vaccine derived polio virus in sewage proves the point.  Although the uptake of polio vaccines is high in UK, there are children who are unimmunised and therefore at risk of developing polio if in contact with this virus.  The risk is small, but it is easily preventable by the vaccine, which in the UK is killed and so cannot cause the disease.  There is no upper age limit for the vaccine.  Anyone who is not fully vaccinated against polio should seek advice from their health visitor or general practice.”


Prof David Heymann, Professor of Infectious Disease Epidemiology, London School of Hygiene & Tropical Medicine, said:

“Vaccine derived polio virus is now present in many countries around the world.  The virus results from a mutation of the Sabin virus that is a live virus used to vaccinate against polio, and it causes paralysis in some, though the majority of infections are asymptomatic.

“Sabin-virus based vaccine (live oral polio vaccine) is now only being used in countries that are in the active eradication phase of polio eradication – other countries have switched to inactivated polio virus vaccine that cannot mutate.

“The fact that it has been found in sewage in the UK attests to the strength of the surveillance programmes of UKHSA.  Its presence in the reminds us that polio eradication has not yet been completed in the world.  The high vaccination coverage using inactivated polio vaccine in the UK will limit the spread of vaccine derived polio and protect those who have been vaccinated against polio paralysis.”



Declared interests

Dr Philip Minor: “I was the Head of the Division of Virology at the National Institute for Biological Standards and Control until I retired in 2017.  My comments have not been shared with the MHRA who now encompass NIBSC and are exclusively my own not those of the MHRA.  I have no conflicts of interest.”

Prof Beate Kampmann: “No COI – except that we have been doing a clinical trial with that new polio vaccine at the MRC Unit in The Gambia, led by a member of my team there, Dr Ed Clarke.”

Prof David Salisbury: “No conflicts.”

Prof Ian Jones: “No conflicts.”

Dr David Elliman: “I have no conflicts of interest.”

Prof David Heymann: “None.”

For all other experts, no reply to our request for DOIs was received.

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