麻豆传媒

In light of the high-profile polio case in Rockland County, New York, and the detection of the virus in wastewater in multiple New York counties, concerns around polio vaccination status have grown, despite decades of ubiquitous early childhood vaccination practices since the polio vaccine was first developed in the 1950s, infectious disease experts said.

It had been nearly 10 years since the U.S. saw a case of polio before an unvaccinated adult man contracted poliovirus type 2 in June, which led to paralysis.

However, most people are immunized against the poliovirus, even if they don't know it -- and that immunity is expected to be life-long, experts told 麻豆传媒.

Amesh Adalja, MD, a senior scholar at the Johns Hopkins Center for Health Security and an infectious disease, critical care, and emergency physician in Pittsburgh, said that those who are uncertain about their polio vaccine status probably do not need to worry.

"I think that it would have taken some effort to not be vaccinated against polio, because it is a routine childhood immunization," he said. "People that are not vaccinated probably would have had some reason not to be vaccinated ... because it's such a standard routine vaccination and required to enter school, that it would be very rare that you were not vaccinated and didn't know it."

The primary approach to preventing another paralytic case of polio relies heavily on population-wide vaccination, which was also the approach used to eradicate wild poliovirus in most countries. The critical distinction is that the current approach does not prevent poliovirus infection completely, but it does effectively prevent the kind of infection that can lead to paralysis or death, noted William Schaffner, MD, a professor of infectious diseases at Vanderbilt University Medical Center in Nashville.

The reason for this, he explained, is because of how the vaccines work. Polio, which is an enteric virus, survives mostly asymptomatically in the intestines and only causes serious complications when the virus manages to enter the bloodstream, where it infects the spinal cord. Without vaccines, this can occur in one out of every 300 to 400 people who are infected, he said.

To prevent this outcome, there are two types of vaccines for polio, an oral polio vaccine (OPV) and an injectable polio vaccine (IPV), but they achieve that result very differently. The OPV contains a live attenuated poliovirus designed to harmlessly live in a person's intestinal tract and rarely enters the bloodstream. The IPV contains dead virus material and enters directly into the bloodstream to provide immunity. Schaffner noted that while both effectively prevent severe infection in the spinal cord, neither prevent infection in the intestinal tract.

"Every person that this virus encounters in New York is not susceptible, the vast majority of them are protected, they're immune, so it goes into their intestinal tract, goes out, and doesn't bother the person who's been infected," he explained. "But this virus is out there circulating."

It is possible, however, for a vaccinated individual to develop a symptomatic polio infection. Still, Schaffner noted that medical consensus is that vaccines provide life-long immunity to the paralytic effects of the virus, but he noted that data on people who had the vaccine 40, 50, or 60 years ago are limited.

One important caveat, he added, is that the oral vaccine can lead to vaccine-derived poliovirus, which can enter the blood and paralyze an unvaccinated person. This is how the person in New York became infected with polio and suffered paralysis, he said. However, as Schaffner and Adalja highlighted, most people are vaccinated against polio, so the real risk is for any unvaccinated individuals.

"The vast majority of people in this country are vaccinated. However, there are pockets of individuals who are not vaccinated, and those people should take it seriously," Adalja said. "If you're one of those individuals [who] have not been vaccinated, this is a threat to you."

He advised people who are unsure about their vaccine status to contact their childhood physician or schools, which should have records about vaccine status as part of the enrollment requirements.

According to the New York City Department of Health (NYCDOH), all children are recommended to receive four doses of the polio vaccine by age 6 -- the first dose before the age of 2 months, the second by 4 months, the third between 6 months and 18 months, and the final dose between 4 and 6 years. Most children older than 6 years have received all four doses, Schaffner said.

He noted that the NYCDOH also showing that a large percentage of children are not up-to-date on their polio vaccine schedule. In fact, the department said in a press release last week that nearly 14% of children ages 6 months to 5 years do not have the three recommended doses of the vaccine.

With poliovirus circulating, as revealed by the wastewater detection study, young children, especially those in New York City, have become one of the most important groups on which to focus public health efforts.

"That's largely because children all over this country were locked in at home during COVID," Schaffner said. "They didn't see their pediatricians and family doctors as frequently, so they fell behind in their routine vaccinations. Now, the public health departments are sending out messages to everybody [to] make sure your children are completely vaccinated."

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