Remains of the polio virus were discovered this summer in wastewater samples in New York, London and Jerusalem. Is the virus on the rise? “We should never be complacent when it comes to infectious diseases,” warns Marc-Alain Widdowson of the Tropical Institute.
Polio or poliomyelitis was once one of the most feared childhood diseases, but thanks to the World Health Organization’s (WHO) large-scale vaccination campaign for children it was declared eradicated in Europe in 2002. Only a few countries in Asia and Africa are still have the extremely contagious intestinal virus. This means that the rest of the world is not yet out of the danger zone. In most cases (90 to 95 percent) the nerve infection is asymptomatic, meaning it causes no symptoms. In rarer cases, symptoms can be severe, such as muscle paralysis and meningitis. This summer, an unvaccinated American in New York was paralyzed with an infection and the virus was found in the sewage of New York, London and Jerusalem.
Is it a surprise that the polio virus shows up in the wastewater of Western countries?
Marc-Alain Widdowson, director of the Antwerp Institute of Tropical Medicine: ‘It is unexpected, but not entirely surprising from a biological point of view. Viruses always come up with something new and can always surprise us. We should never be complacent when it comes to infectious diseases. Polio looks like a disease of the past or something that only occurs in the tropics, but suddenly it’s on our doorstep again. While there are no confirmed cases of paralysis in Europe, this is a worrying evolution that needs to be closely monitored. ‘
Why is the virus re-emerging?
Widdowson: ‘The virus we now see in sewage and are concerned about is the’ vaccine-derived polio virus’ or VDPV. This is a virus spread by someone who was recently vaccinated against polio with a weakened but still alive form of the virus. The disadvantage is that in rare cases this vaccine virus can reactivate and mutate and then circulate among unvaccinated individuals. It can start to resemble the original polio virus and still cause paralysis. In addition, you also have three types of wild polio virus, two types have been eradicated, but type 1 polio virus still occurs in an area on the border between Afghanistan and Pakistan. In the past, this type has only sporadically spread to other parts of the world, such as Malawi and Mozambique. But those outbreaks are under control. ‘
The British health authorities call it a “national accident”, the Americans call it the “greatest threat of polio in a long time”. Should we be worried?
Widdowson: ‘There is no need to panic. The risk of polio becoming an endemic problem in Europe and the United States is very limited, but what the British and American authorities want to avoid is that the virus continues to circulate in under-vaccinated populations, who can develop paralysis. ‘
Is it also possible that the vaccine-derived poliomyelitis virus is also present in wastewater in Belgium?
Widdowson: ‘It cannot be ruled out that VDPV circulates in Belgium and is therefore present in our waste water. It is therefore extremely important that the situation is constantly monitored. Vaccination coverage in Belgium is on average very high in most places, so hopefully it will be enough to prevent a possible outbreak of VDPV in society. But also when it comes to vaccination, we must not rest too much on our laurels. We still lack groups of people, such as religious minorities or people who refuse vaccination for other reasons. ‘
Why are attenuated and still alive viruses used for the polio vaccine?
Widdowson: “There are two good polio vaccines: the” inactivated polio vaccine “or IPV uses a dead polio virus to induce immunity. The oral polio vaccine or OPV contains a live, but weakened virus. OPV has the advantage. to prevent the spread of polio because vaccinated people shed the vaccine virus in their feces, thus exposing unvaccinated people to the environment. This was a good thing, especially at the start of global vaccination programs. In this way, the vaccine it could indirectly immunize family members against wild polio when they come in contact with feces. Now that we have a very low number of polio patients, this phenomenon gradually begins to be seen as a bigger problem. “
Can the existing oral polio vaccine be made safer?
Widdowson: ‘Something has already happened. Since most of the VDPV is derived from the type 2 polio virus, the OPV vaccine contains only type 1 and type 3 since 2016. In addition, more and more countries are switching to the IPV vaccine with the virus dead. Belgium already did this in 2001. The intention is to only use IPV worldwide in the long term. But there is a troublesome problem. Today, if you have a VDPV outbreak, you need to re-use the vaccine that initially caused the problem – the oral vaccine with the type 2 strain. This adds more vaccine virus which in turn can mutate again. . This is what makes the polio vaccination schedule such a complicated issue. Fortunately, there is now also a new oral vaccine with a type 2 strain that is no longer so mutable. This was tested by the team of vaccinologist Pierre van Damme, among others. ‘
The fight against polio in Pakistan and Afghanistan is particularly crucial to the ultimate eradication of polio. Where are we with that?
Widdowson: ‘It is important that vaccination teams can continue to operate in the Pakistan-Afghanistan border area, where wild polio is still an endemic disease. This is a logistical undertaking because it concerns a conflict region where the Taliban have power. Furthermore, the population is suspicious of those vaccination teams because they fear they are spies. This is regrettable, because vaccination programs should be above politics and conflict. If we were able to eradicate the disease, it would be an incredible success. The wild polio virus would therefore be the third most infectious disease, after smallpox and “rinderpest”, which has been suppressed by humans. ‘
What is the vaccination coverage for polio in Flanders?
92.9% of babies born in 2021 received the first dose of the hexavalent vaccine. This vaccine protects against poliomyelitis, diphtheria, tetanus, whooping cough, hepatitis B and hemophilus influenzae type b in the first months of life. For the third dose of the same vaccine, the vaccination rate drops to 89.7%.
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