A particular type of poliovirus is spreading in the United States. The US Centers for Disease Control and Prevention have confirmed that the country is now joins a list of around 30 other countries where virus circulation has been identified. Those countries include the UK, Israel, Egypt, Yemen and about two dozen in Africa.
The news, announced on September 13, comes after the identification in July of a case of paralytic polio in an unvaccinated adult in Rockland County, New York. Public health officials discovered that the case was caused by what is called a vaccine-derived poliovirus (learn more about this type of poliovirus below). This spurred surveillance of sewage in Rockland and surrounding counties, because people shed poliovirus in their feces. The wastewater samples showed that the virus was spreading in Rockland and neighboring areas.
In response, New York Governor Kathy Hochul declared a state of emergency on September 9 to expand access to polio vaccination statewide. Three of the counties where poliovirus has been detected in sewage (Rockland, Orange, and Sullivan) have polio vaccination rates of only about 60 percent. The virus has also appeared in New York City and Nassau County.
While most people infected with polio have no symptoms, some may feel like they have the flu, with fever, fatigue, or a sore throat. In rare cases, the virus can cause permanent paralysis, and the disease can become fatal if the paralysis affects the muscles that control breathing or swallowing. Anyone who is not vaccinated is at risk of contracting paralytic polio if infected.
Widespread vaccination efforts helped eliminate wild polioviruses from the United States in 1979, but public health officials are still working to eradicate the disease globally (Serial number: 09/12/19). New concerns about polio in the United States are fueled by vaccine-derived versions of the virus that spread in areas with low vaccination.
Here are six things you need to know about polio right now.
There are two types of polio vaccines. What is the difference?
Polio vaccines come as a shot, in the arm or leg, or as a liquid by mouth. These vaccines provide protection against wild poliovirus and vaccine-derived poliovirus. Both polio vaccines used to be administered in the United States, but since 2000, the shot has been the only polio vaccine available in the country (Serial number: 10/27/21).
The shot is an inactivated vaccine that is given as part of routine childhood immunizations in the United States. It is made using poliovirus that has been “killed,” stripped of its ability to cause disease. Children receive a total of four injections. The inactivated vaccine protects against paralysis.
The oral vaccine, which is still used in many countries, is an attenuated vaccine, made from live but weakened poliovirus. This vaccine can help prevent transmission of wild poliovirus if a vaccinated person drinks water or eats food that has been contaminated with feces containing the pathogen. That means can prevent the spread of poliovirus in a community while also protecting against paralysis (Serial number: 8/1/21).
But because these attenuated versions can replicate, the virus can spread from cell to cell and possibly to other people. Which brings us to the next question.
What are vaccine-derived polioviruses?
These viruses are related to the oral vaccine. Since the viruses used in the vaccine can replicate, they can spread, but they are too weak to cause serious illness. The problem arises when an attenuated virus from the oral vaccine spreads among too many people and regains its ability to cause paralysis, says Adam Lauring, a virologist and infectious disease physician at the University of Michigan in Ann Arbor. “Because it can replicate, it will evolve.”
In a community with little or no polio vaccination, these vaccine-derived polioviruses can cause illness.
So why do some countries still use the oral vaccine?
the Global Polio Eradication Initiative, which includes the World Health Organization, the CDC, the United Nations Children’s Fund and other groups, has worked since 1988 to eradicate polio. The oral vaccine has been a key tool in global efforts to eliminate polio, says Lauring. That’s not only because the vaccine is cheap and easy to use in low- and middle-income countries, but also because studies suggest it best protects the gut, the part of the body where the virus grows. The more protected the intestine is, the greater the chances of reducing transmission and stopping an outbreak.
What does it mean that poliovirus is being detected in wastewater?
It is a sign that the poliovirus is spreading among people in those regions.
Paralysis caused by poliovirus is rare, affecting around 1 in 200 infected people. So the single case of paralysis identified in New York in July was already an indication that there could be hundreds of other infections. Since then, the virus has been detected in wastewater samples since May. The continued presence of the virus in sewage suggests that people are still getting infected and passing it on to others.
Should unvaccinated people be vaccinated?
Yes. “If you don’t know if you’ve had polio shots, then you probably should get a polio shot,” says Lauring. “If you didn’t [get vaccinated]You should get vaccinated against polio.”
Vaccine-derived polioviruses are largely a problem in communities where not enough people are being vaccinated. “That’s one piece of the puzzle of what’s been going on in New York,” says Lauring. Low immunization rates mean that vaccine-derived viruses can spread, mainly among unvaccinated people, and circulate silently before someone gets sick.
Places that have sanitation problems or struggle with other intestinal diseases are also hotspots for vaccine-derived polioviruses. When there is not enough immunity to stop poliovirus circulation, the virus can further evolve.
What about people who got vaccinated as children?
People who got vaccinated, even decades ago, are likely still protected.
Adults who are at high risk of exposure to the virus. are eligible for a lifetime booster shot, according to the CDC. Otherwise, people should make sure they have received all recommended doses.
Exactly how long childhood polio vaccines are in protecting against serious disease in adults is unknown. With little polio circulating in the world, it’s a difficult question to study, says Lauring. Still, for years there haven’t been any cases of polio in the United States, and we’ve largely had immunity from the inactivated vaccine, she says. “I’m not ringing alarm bells.”