Health authorities in the U.K. are urging residents to get vaccinated against poliovirus after the virus was found in sewage samples in London.
The virus was detected as part of routine surveillance, the UK Heath Security Agency (UKHSA) said in a press release. And, while the agency says that it’s normal for one to three “vaccine-like” polioviruses to be detected each year, “these have always been one-off findings that were not detected again.”
The previous detections happened when “an individual vaccinated overseas with the live oral polio vaccine (OPV) returned or travelled to the UK and briefly ‘shed’ traces of the vaccine-like poliovirus in their feces,” the release says. But the latest viruses detected in sewage has “continued to evolve and is now classified as a ‘vaccine-derived’ poliovirus type 2 (VDPV2), which on rare occasions can cause serious illness, such as paralysis, in people who are not fully vaccinated,” the UKHSA says.
The detection of these polioviruses “suggests it is likely there has been some spread between closely-linked individuals in North and East London and that they are now shedding the type 2 poliovirus strain in their feces,” the release says.
The UKHSA stresses that the virus “has only been detected in sewage samples and no associated cases of paralysis have been reported” but that “investigations will aim to establish if any community transmission is occurring.”
As a result of the detection, the UKHSA is urging people who are not up to date with their poliovirus vaccination to get vaccinated against the virus.
It’s understandable to have questions about poliovirus after hearing this. Here’s what you need to know.
What is poliovirus?
Poliovirus is a virus that causes the potentially disabling and life-threatening disease, polio, according to the Centers for Disease Control and Prevention (CDC). The virus spreads from person to person and can infect a person’s spinal cord, leading to paralysis.
Polio caused widespread panic in the U.S. in the late 1940s, when outbreaks caused an average of more than 35,000 people a year to become disabled, the CDC says. However, a successful vaccination program has made the U.S. polio-free since 1979.
“It is a vaccine-preventable disease,” says Thomas Russo, M.D., professor and chief of infectious disease at the University at Buffalo in New York. “We’ve been trying very hard to eradicate it. We’ve been close but it’s stubbornly hanging out in a few countries.”
Vaccine-derived poliovirus, which was detected in the U.K., is slightly different from the wild poliovirus that caused widespread fear in the 1940s. It’s a strain of the weakened poliovirus that was initially included in oral polio vaccine (OPV), the CDC explains. Vaccine-derived poliovirus has changed over time and behaves more like the wild virus.
“The vaccine that’s still widely used over much of the world is a live, tamed version of the poliovirus given in drops on a sugar cube,” says William Schaffner, M.D., an infectious disease specialist and professor at the Vanderbilt University School of Medicine. “It goes into the GI tract, multiplies, and we produce antibodies against polio.” But, because this is a live virus, Dr. Schaffner says it can mutate. “It has the potential to mutate back to a strain that can behave as though it were the wild virus and cause disease in people who are unvaccinated,” he says.
For what it’s worth, the U.S. now gives the inactivated polio vaccine (IPV), which won’t shed polio in poop that can mutate or spread.
“These vaccine-derived strains will always be an issue so long as the OPV vaccine is used, because that vaccine is designed to induce viral shedding,” says Amesh A. Adalja, M.D., a senior scholar at the Johns Hopkins Center for Health Security. “In certain instances, vaccine-derived poliovirus can cause infection in unvaccinated individuals.”
What symptoms does poliovirus cause?
Most people who are infected with poliovirus—about 72%—will not have any visible symptoms, the CDC says. But about 25% will develop flu-like symptoms that include:
- Sore throat
- Stomach pain
The symptoms usually last for two to five days and then go away on their own, the CDC says. A smaller portion of people (less than 1%) will develop more serious symptoms that impact the brain and spinal cord, including:
- Paresthesia (feeling pins and needles in the legs)
- Meningitis (an infection of the covering of the spinal cord and/or brain)
- Paralysis or weakness in the arms, legs, or both
How is poliovirus transmitted?
Poliovirus is highly contagious and spreads through person-to-person contact, the CDC says. The virus lives in an infected person’s throat and intestines and can be spread through contact with the poop of an infected person or droplets from a cough or sneeze of an infected person.
An infected person can spread the virus to others right away and up to two week after symptoms appear, the CDC says. It can also live in a person’s poop for several weeks.
How is poliovirus treated?
There is no treatment for poliovirus, Dr. Adalja says. However, there is a vaccine for it that’s included as part of the routine childhood vaccination series.
Almost all children—99% to 100%—who get all the recommended doses of the inactivated polio vaccine will be protected from polio, the CDC says.
How concerned about poliovirus should you be?
Experts say you shouldn’t panic about this news, but you should make sure you and your family have been fully vaccinated against poliovirus. “Make sure your child is up to date with their vaccines and everything will be OK,” Dr. Russo says.
Dr. Schaffner says the detection of poliovirus in the U.K. is an example of “careful surveillance” that allows public health officials to act quickly. “It’s another example of public health at its best,” he says.
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