Polio is Back in the U.S. Here’s How to Stay Safe
uUntil recently, polio was a relic of history in the United States. Once a scourge that paralyzed or killed up to tens of thousands of children each year, the US officially declared the disease eradicated in 1979 thanks to widespread vaccination.
But polio is back. On July 21, the New York State Department of Health and Human Services announced a case of polio in an unvaccinated man in Rockland County. Poliovirus has since been found in sewage in Rockland and neighboring Orange County, as well as in New York City.
The development has given rise to justifiable concern. “Even a single case of paralytic polio represents a public health emergency in the United States,” writes a group of researchers in a report published Aug. 16 in the Morbidity and Mortality Weekly Report. The bottom line is that anyone who is not fully vaccinated against the disease should educate themselves about vaccinations immediately. Here’s what the resurgence of polio in the US means for your health.
A Brief Recent History of Polio
As recently as 1988, polio was a global threat: according to the World Health Organization (WHO), it was endemic in 125 countries and caused an average of 350,000 cases of paralysis or death each year. That year, the World Health Assembly established the Global Polio Eradication Initiative with the goal of eradicating the disease, just as smallpox was officially eradicated in 1980.
The way to end polio would be the same as smallpox: global vaccination. The strategy worked exceptionally well. Today, polio is endemic in just two countries — Afghanistan and Pakistan — which have had just 18 cases so far this year, according to the initiative. But there are problems with this overall success story, and they pertain to the vaccination campaign itself.
What is vaccine-associated polio?
There are two types of polio vaccine: oral polio vaccine (OPV), which, as the name suggests, is administered by drops in the mouth; and the inactivated polio vaccine (IPV), which is administered by injection. The IPV uses a killed poliovirus to familiarize the immune system with the disease and prepare it to respond if it ever encounters a live virus. The OPV uses a weakened virus that’s weakened enough that it can do the same job of priming the immune system without actually causing the disease.
The major benefit of OPV is that it is cheaper and much easier to administer, making it the vaccine of choice for mass vaccination campaigns. The downside is that in extremely rare cases, the weakened virus can become virulent again, causing illness in the person who received the drops, or the revived virus being excreted in the infected person’s feces and circulating in the sewage – what leading to the possibility of so-called vaccine-associated polio in others.
Reversion to virulence is rare. Since 1988, vaccination has prevented an estimated 18 million cases of polio and saved 1.5 million lives, according to the US Centers for Disease Control and Prevention (CDC). According to UNICEF, 10 billion OPV doses have been administered worldwide since 2000. By these numbers, vaccine-caused polio is low-risk, with a total of 540 cases worldwide this year – not including the US case – and a recent peak year in 2020, when 1,100 cases were reported worldwide. Typically, there are far fewer cases in any given year.
In order to eliminate the problem domestically, the US stopped using the OPV in 2000 and switched to IPV exclusively. But that doesn’t stop vaccine-derived strains from being imported by overseas travelers or by a US citizen who has traveled internationally, picked up the virus from someone who had received the OPV, and brought it home. Typing of the virus found in the Rockland County man showed that it was indeed a vaccine-derived strain that caused the disease.
No matter how the virus got here, it’s among us now — and it’s by no means necessarily confined to water supplies in just three New York boroughs. If a traveler could put it in a state, other travelers could take it anywhere.
“The fact that we’re finding it in sewage shows it’s more common than people think,” says Ian Lipkin, professor of epidemiology at Columbia University’s Mailman School of Public Health. “We’re looking at the tip of the iceberg.”
Columbia University School of Medicine virologist Vincent Racaniello adds: “I suspect it’s already happening in many, many places in the US. In fact, I think if we look in every major city in the US, we’re going to find vaccine-derived polio in the sewage for sure.”
Polio vaccination rates are shockingly low
Immunization guidelines require that children receive three polio shots by age two to be considered fully vaccinated. But polio vaccine uptake in the US is insufficient. In Rockland County, just over 60% of eligible children received their three doses. (These rates vary widely within the county; in one zip code, only 37% of children are vaccinated, according to the Aug. 16 report.) In Orange County, fewer than 59% of children are fully vaccinated. In New York City, rates are much higher at around 86%, but the average varies by borough, with Manhattan reaching 91% and Brooklyn lagging the other boroughs at 81%. Nationwide vaccination rates are just under 79%.
Nationwide, the numbers are higher, with 92.6% of children by the age of two being fully vaccinated, according to the CDC. But here too there are local differences; For example, only 79.5% of children in Oklahoma are fully vaccinated, along with 80.3% in South Carolina. That worries experts, because every unvaccinated child runs the risk of becoming a polio victim – and a reservoir for the virus. For every case of paralytic polio, up to 200 other people are likely to be infected, who either show no signs of the virus or have mild cold- or flu-like symptoms. Each of them is a walking viral vector.
“Most people who are infected with polio have no symptoms,” says Lipkin. “They don’t even know they’re infected, but they can transmit the disease.”
Even people vaccinated against the disease with IPV — the only type of polio vaccine used in the United States — can potentially shed the virus. The OPV establishes what is known as gut immunity, which means that – assuming a person is not one of the few in which the poliovirus returns to its virulent state – viral replication does not occur in the gut system and therefore no infectious virus is shed in the feces. However, because IPV must be injected to be effective, it does not offer gut immunity, meaning that if an IPV vaccinated person ingests a vaccine-derived strain, this active virus can multiply in the gut and be shed.
This poses no health risk to an IPV vaccinated person, but they may unintentionally spread the virus if exposed to it. “You don’t develop polio” if you have the IPV vaccine, “because once the virus got into your blood, your immune system would take care of it,” says Racaniello. “But the virus can multiply in your gut and you can excrete it and it can end up in the sewer that way.”
What you can do to reduce your risk
The resurgence of polio does not necessarily mean that a nationwide spread of the disease is imminent. But it’s a wake-up call that unvaccinated children and adults need to get their shots now. “The solution to the problem is to make sure you’re vaccinated,” says Racaniello. “Because if you’re vaccinated, you won’t get polio.”
But the COVID-19 pandemic has exposed that the wisdom of getting vaccinated against an infectious disease can clash hard with politics, claims to personal liberty, and unfounded rumors about vaccine safety and effectiveness. Even before the pandemic, there was a strong anti-vaccine community in the US, and that cohort has not gone away. “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.”
The good news is that both polio vaccines are remarkably effective and long-lasting. If people received a full course of either vaccine when they were children, they do not need a booster now. “Anyone who has had a full polio vaccination course doesn’t need a booster,” says Racaniello. “The immunity to polio conferred by vaccination lasts for life.” This, he points out, is true whether you received either IPV or OPV in childhood.
That doesn’t mean that polio booster shots are never necessary. People traveling to high-risk areas like Afghanistan, Pakistan, or any of the countries that have experienced high rates of vaccine-caused polio — like Nigeria, which has 238 of the world’s 540 cases this year — should start with a booster, Lipkin says .
However, for most people, the resurgence of poliovirus in the US poses no threat thanks to the simple preventive tool of vaccination. They beat the disease once in the US and now, nationally, they are working to do it again.
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