UPolio was a historical relic in the United States. It used to be a terrible disease that killed thousands of children each year. The U.S. finally declared it eradicated in 1979 thanks to mass vaccinations.
Polio has returned. A case of polio was reported by the New York State Department of Health on July 21. Since then, poliovirus was found in Rockland County and Orange County as well as New York City’s wastewater.
There is cause for alarm. “Even a single case of paralytic polio represents a public health emergency in the United States,” write a group of researchers in a report published Aug. 16 in the Weekly Report on Morbidity & Mortality. It is important that everyone who has not been vaccinated for the disease is up to date. Here’s what to know about what polio’s re-emergence in the U.S. means for your health.
Here’s a brief history of polio.
According to the World Health Organization, polio had been a global problem since 1988. It was an epidemic in 125 countries, with 350,000 cases of paralytic or fatalities each year. The Global Polio Eradication Initiative was established by the World Health Assembly in 1988. Its goal is to eradicate the disease as well as smallpox.
Worldwide vaccination would provide the means for ending polio. It has been extremely successful. Today, polio is endemic in just two countries—Afghanistan and Pakistan—which have seen just 18 cases between them so far this year, according to the Initiative. There are also problems in this success story. They involve vaccination campaigns.
What exactly is vaccine-derived, poliomyelitis?
Two types of polio vaccine are available: one is the oral polio vaccination (OPV), administered via drops into the mouth, and another is the injectable inactivated poliovaccine (IPV). To familiarize the body with the virus and prepare it for the eventual encounter with a live one, the IPV injects dead poliovirus. The OPV uses an attenuated virus—weakened to the point that it can do the same work of priming the immune system without actually causing the disease.
The OPV has the advantage that it’s cheaper and easier to administer. This makes it an ideal vaccine for mass vaccination campaigns. The disadvantage is that on exceedingly rare occasions, the weakened virus can revert to virulence, causing the disease in the person who received the drops or allowing the revived virus to be shed in feces of the infected person and circulate in wastewater—leading to the possibility of so-called vaccine-derived polio in others.
Rarely does virulence revert. The U.S. Centers for Disease Control and Prevention have estimated that vaccinations have prevented 18 million cases from polio and have saved the lives of 1.5 million people. UNICEF reports that 10 billion doses OPV were administered globally since 2000. Measured against those numbers, vaccine-derived polio is low-risk, with a total of 540 global cases so far this year—not including the U.S. case—and a recent peak year occurring in 2020, when 1,100 cases were reported globally. There are usually far fewer cases than there is in any given year.
In 2000 the United States stopped using the OPV and switched exclusively to the IPV. But that doesn’t prevent vaccine-derived strains from being imported by travelers from overseas, or by a U.S. resident who traveled internationally, picked up the virus from someone who had received the OPV, and brought it back home. It was a vaccine-derived virus, according to typing of the Rockland County resident.
No matter how the virus got here, it is now among us—and it is by no means necessarily limited to the water supply in just three New York regions. Travelers could easily bring the virus into any other state.
“The fact that we’re finding it in wastewater tells you it’s more common than people appreciate,” says Ian Lipkin, professor of epidemiology at Columbia University’s Mailman School of Public Health. “We’re looking at the tip of the iceberg.”
Adds virologist Vincent Racaniello of the Columbia University School of Medicine: “I suspect it’s already in many, many places in the U.S. In fact, I think that if we look in every major city in the U.S., we will find vaccine-derived polio in the sewage for sure.”
The rates of polio vaccination are alarmingly low
To be fully vaccinated, children must receive at least three doses of polio vaccines by the age of two. However, the U.S. is not achieving sufficient polio vaccination coverage. Just over 60% of Rockland County’s eligible children have had their three doses. The Aug 16 report shows that only 37% are fully vaccinated in one zipcode. Orange County has a lower percentage of fully-vaccinated children at 59%. New York City has rates that are higher at around 86%. However, they vary by borough. Manhattan is at 91% while Brooklyn trails at 81%. Only 79% of the state’s vaccination rates are above 79%.
According to the CDC, this number is higher in America, where 92.6% are fully vaccinated at the age of 2. However, these numbers are not uniform across the country. In Oklahoma for instance, only 79.5% and South Carolina at 80.3% are both fully vaccinated. That worries experts because every unvaccinated child is at risk of becoming a polio victim—and a reservoir for the virus. Up to 200 others could be infected with paralytic polio. They may also have mild symptoms or no symptoms. They are all a virus vector.
“The majority of people who are infected with polio have no symptoms,” says Lipkin. “They aren’t even aware that they are infected, but they can transmit the disease.”
Even people who have been vaccinated against the disease with the IPV—which is the only type of polio vaccine used in the U.S.—can potentially shed the virus. The OPV establishes what’s known as gut immunity, meaning that—assuming a person is not among the few who in whom the poliovirus reverts to its virulent state—there is no viral replication in the intestinal system, and therefore there is no infectious virus shed in feces. Because it has to be injected, the IPV does not give gut immunity. If an IPV-vaccinated patient picks up an active virus strain from the vaccine, the virus will reproduce and then be shed.
The IPV vaccine does not pose a health risk for the person who has been vaccinated. However, they could unintentionally increase the chances of getting the virus. “You do not develop polio” if you have the IPV vaccine, “because once the virus enters your blood, your immune system would take care of it,” says Racaniello. “But the virus can reproduce in your gut and you can shed it and it can end up in sewage that way.”
How to lower your risk
However, the reemergence of polio doesn’t necessarily indicate that there will be a widespread spread. This is an alarming sign that all unvaccinated adults and children need to be vaccinated. “The solution to the problem is just making sure you’re vaccinated,” says Racaniello. “Because if you’re vaccinated, you will not develop polio.”
The COVID-19 epidemic has shown that the wisdom in getting vaccinated for an infectious disease is not always wise. It can be a stumbling block to politics and personal freedom as well as unfounded rumors and doubts about its safety and effectiveness. Before the epidemic, the U.S. had a strong anti-vaccine group. That number has not diminished. “There are all sorts of bizarre conspiracy theories that have been put forward by one group or another,” says Lipkin. “It’s a huge problem.”
Good news! Both polio vaccines work well and last a long time. People who have had both polio vaccines as children do not require a booster. “Anyone who has had a complete polio vaccination series does not need a booster,” says Racaniello. “Immunity to polio conferred by vaccination lasts a lifetime.” This, he stresses, is true whether you received either the IPV or the OPV in childhood.
That doesn’t mean that polio boosters are never necessary. People traveling to high-risk areas, like Afghanistan, Pakistan, or any of the countries that have seen high rates of vaccine-derived polio—such as Nigeria, which is home to 238 of the 540 global cases this year—should first receive a booster, says Lipkin.
The simple preventative vaccines have made it so that the risk of poliovirus returning to the U.S. is minimal for the majority of people. The Americans defeated it once and are now able to do the same in other countries.
Here are more must-read stories from TIME
