Vaccine-Derived Polio: What to Know After 1st Case in Nearly a Decade Identified in New York

The first U.S. case of polio in nearly a decade has been identified in New York state, officials announced Thursday.

A joint press release from the New York State Department of Health and the Rockland County Department of Health confirmed that the patient—an unvaccinated man in Rockland County—picked up the virus via transmission chain originating with someone who had received the oral polio vaccine (OPV). It's an instance of an infection with vaccine-derived poliovirus (VDPV).

Because OPV is no longer authorized or administered in the U.S.—the states have only used the inactivated polio vaccine (IPV) since 2000—officials believe the virus originated outside of the U.S., where the oral vaccine is still given.

Although the unidentified patient is "no longer contagious," officials said they are now focused on vaccinating the unvaccinated population, and determining if anyone else has been infected by the virus.

"Based on what we know about this case, and polio in general, the Department of Health strongly recommends that unvaccinated individuals get vaccinated or boosted with the FDA-approved IPV vaccine as soon as possible," State Health Commissioner Mary T. Bassett, MD, MPH, said in the press release. "The polio vaccine is safe and effective, protecting against this potentially debilitating disease, and it has been part of the backbone of required, routine childhood immunization recommended by health officials and public health agencies nationwide."

What Is Polio?

Polio, or poliomyelitis, is a potentially disabling and life-threatening disease caused by the poliovirus, according to the Centers for Disease Control and Prevention (CDC). The virus can infect a person's spinal cord, leading to paralysis.

Polio caused panic in the U.S. in the late 1940s, when outbreaks led to an average of more than 35,000 people a year (mostly children) to become disabled—including President Franklin Delano Roosevelt. But a vaccine was developed and widely distributed, making the U.S. free of polio since 1979.

The virus is highly contagious and spreads from person to person through contact with an infected person's feces or droplets from a cough or sneeze. Once infected, a person can spread the virus before symptoms appear, up to two weeks after the onset of symptoms, and even if they are asymptomatic.

While most people who get infected with poliovirus won't have visible symptoms, around 25% will show flu-like symptoms, according to the CDC. Those symptoms can include:

• Sore throat
• Fever
• Fatigue
• Nausea
• Headache
• Stomach pain

But a small portion of people—less than 1%—will develop serious symptoms that impact the brain and spinal cord. Those include:

• Paresthesia (a pins-and-needles feeling in the legs)
• Meningitis (an infection of the covering of the spinal cord and/or brain)
• Paralysis (inability to move parts of the body)

Vaccine-Derived Polio vs. Wild Polio

The patient in New York contracted a form of the virus known as vaccine-derived poliovirus—a different strain than wild poliovirus, for which vaccines were developed. Vaccine-derived poliovirus is a strain of the weakened poliovirus initially included in the oral poliovirus vaccine, according to the CDC.

Because the oral poliovirus vaccine contains that weakened strain of polio, immunized people can excrete it in their stools or respiratory secretions, allowing it to infect other people. This risk is why the U.S. stopped using the oral vaccine in 2000, and now exclusively uses the inactivated poliovirus vaccine, which does not use a live version of the virus.

Over time, vaccine-derived poliovirus has changed, allowing it to behave more like wild poliovirus. "It can mutate and has the potential to cause disease in individuals," Thomas Russo, MD, professor and chief of infectious disease at the University at Buffalo in New York, told Health. "In almost all of these vaccine-derived cases, it mutates and becomes more virulent."

While the risk of vaccine-derived polio is low in the U.S., it does have the potential to spread in other countries that still use the oral poliovirus vaccine—and in order to globally eradicate polio, the world would have to discontinue use of that vaccine.

"In my opinion, [vaccine-derived polio] should be considered a separate problem than wild polio," Amesh A. Adalja, MD, a senior scholar at the Johns Hopkins Center for Health Security, told Health. "So long as Sabin vaccine [the oral poliovirus vaccine] is used in parts of the world, this will always be a risk."

Unvaccinated Individuals Are at the Highest Risk

The inactivated poliovirus vaccine is part of routine childhood vaccinations in the U.S. The CDC recommends children four doses of the polio vaccine at the following ages:

• 2 months old
• 4 months old
• 6–18 months old
• Booster dose at 4–6 years old

Additionally, adults who are traveling to places with an increased risk of polio, and who are unvaccinated, incompletely vaccinated, or have an unknown vaccination status are recommended to receive three doses at the following intervals:

• Two doses separated by 1–2 months
• One dose 6–12 months after the second dose

Even adults who have been fully vaccinated against polio but are traveling to high-risk areas are recommended to receive a one-time booster dose.

However, not all people in the U.S. have been vaccinated. "The unvaccinated—especially young children—are at risk," Richard Watkins, MD, an infectious disease physician and a professor of medicine at the Northeast Ohio Medical University, told Health.

In that case, the New York case of polio "is a good wakeup call," Dr. Russo said. "With COVID, some families got behind on pediatric vaccines. If you missed your children's vaccines, go ahead and get vaccinated."

But overall, for vaccinated people, this new case of polio is not a huge concern. "We are highly vaccinated in this country," William Schaffner, MD, an infectious disease specialist and professor at the Vanderbilt University School of Medicine, told Health. "The attention right now is really directed to contacts of this person."

In response to the case of polio, Rockland County is holding a vaccine clinic today and Monday for anyone who is unvaccinated, did not complete a poliovirus vaccine series, or are concerned they may have been exposed. People who are at risk of being exposed may also receive a booster dose of the vaccine.