One case – and evidence in the sewage of greater spread – may not seem significant, and Americans are highly vaccinated against polio, meaning most people are protected from paralysis. According to the latest data from the US Centers for Disease Control and Prevention, more than 92% of children in the United States have received polio vaccination by the age of 2.
But there is a reason why even a single case puts health officials on alert. The uninfected and under-vaccinated are at risk for serious disease, but the spread may not be as clear – partly because of a vaccine switch that happened more than two decades ago.
Vaccinated people are not in harm’s way if they catch poliovirus, which is spread through the fecal-oral route from the human intestinal tract: a person gets fecal germs on their hands, touches something or someone else. shake hands with the person, and that person puts the contaminant on their hands in their nose or mouth. This is why young children – those still in diapers – are particularly susceptible to infection.
The poliovirus can infect cells in the intestine and cause a mild illness – cramps, diarrhea or constipation. Occasionally, however, the virus will slip through the intestinal barrier and into the bloodstream, where it will home onto motor neurons in the spinal cord — cells that tell muscles to move. When the virus infects these cells, it destroys them, causing lifelong paralysis in people.
Doctors estimate that there is one case of paralytic polio for every 300 to 1,000 mild infections.
a tale of two vaccines
Until the year 2000, two types of vaccines were used to vaccinate Americans against polio – vaccine droplets, sometimes given on sugar cubes, which are made from live, weakened poliovirus, and one Injectable vaccine that uses killed polio virus.
There are several important differences between vaccines, but a major one is that the oral vaccine induces so-called mucosal immunity, so that if a vaccinated person is ever exposed to poliovirus, they do not have copies of themselves in their gut. can be made, and will not be given to anyone else.
However, there is also a downside to using the oral vaccine.
A pediatrician and vaccine researcher at the Maryland School of Medicine’s Center for Vaccine Development and Global Health, Dr. James Campbell said, “The big drawback of the oral polio vaccine is that you skip it.”
Very rarely, given once every 3 million times, the weakened virus in the oral vaccine can escape the gut and cause paralysis.
The weakened virus can also pass in the stool, and rarely, it mutates and turns back into a virus form that can cause paralysis, especially if the virus is being transmitted where there is poor hygiene and low vaccinations. is the rate.
“So even when we were preventing polio with this vaccine, we were rarely causing vaccine-associated polio myelitis,” said Dr. William Schaffner said.
That’s what happened to the young adult in New York. Genetic sequencing revealed that the virus that paralyzed him originated from an oral vaccine, which is still used in other countries.
The injected vaccine, which uses the killed virus, cannot be converted back into a harmful form. While the oral vaccine is relatively safe, the injected vaccine is even safer.
In 2000, public health officials decided that the US should only use shots to vaccinate against polio, which contain the inactivated virus.
Some vaccinated people can spread the virus
However, there is a drawback to using the injected vaccine. Although it prevents paralysis, it does not necessarily prevent infection.
Because of this, young adults and children vaccinated because Switch can still be infected with poliovirus in their intestines and shed the virus in their stool.
“They are protected from a paralytic disease, but they can still harbor the virus and spread it to others. And that’s the situation we have in New York now,” Schaffner says.
“So you can essentially get the whole community carrying this virus in their intestines, but they don’t even know it’s there.”
Schaffner says it’s not a big problem if everyone around them is also safe. But the fear is that silent transmission could carry the virus into the pockets of people who haven’t been vaccinated against polio, and they could wind up with more dire consequences.
“In highly unvaccinated communities, especially when there are too many people living in one place without vaccinations, it just gives the virus an opportunity to shed and pass on to the person more commonly,” Campbell says.
One group that may be at risk are children. Children are usually given four polio vaccines before the age of 6. They get a third shot at 2 months, 4 months of age, between 6 and 18 months of age, and a fourth shot between 4 and 6 years of age.
Schaffner says that children who are up to date on their vaccines but have not yet been fully vaccinated may be at increased risk of polio infection, but no one really knows.
“The answer, clearly, is that they are partially preserved,” Schaffner said.
“It’s the whole range that gives you complete protection,” he said. “We are nervous about children who are in vaccine progress, but not yet well enough to receive all vaccines.”
Push for more vaccinations
Officials in New York say vaccination for all is key to making sure the virus doesn’t disable more Americans.
“Our single case of polio may be the tip of the iceberg, we don’t know,” Rockland County Executive Ed Day said in a video posted to Facebook. “As you can see, it could turn into a little wildfire.”
“This only happens if people are not vaccinated,” he said.
(This story has not been edited by seemayo staff and is published from a rss feed)