During the mid-twentieth century, the polio epidemic was so severe in the United States that tens of thousands of people were crippled by it every year. Once virologist Dr. Jonas Salk created a successful vaccine in 1955, however, those numbers began to plummet. Since 1979, there has not been a single case of wild poliovirus that has originated in the United States. (Some wild poliovirus cases have been brought to the United States from other countries.) Even today, polio cases of any kind in this country are strikingly rare.
Yet a new crop of polio cases in New York state suggests that polio outbreaks are no longer as rare as they once were in the United States.
A federal team of scientists has been sent to New York by the Centers for Disease Control and Prevention (CDC) to investigate what appears to be a string of polio cases in the state. It began in Rockland County, where a once-healthy young adult saw their legs become paralyzed after developing the first case of polio seen here in almost a decade. That patient is believed to have received polio from an oral vaccine, the type of which are not administered in the United States any longer but are still used outside the country. The oral vaccine uses a live weakened version of the poliovirus.
News of a polio outbreak in the United States is unprecedented given the near-eradicated state of the disease. Polio vaccines are a standard complement of vaccines issued in the American health care system; most children in the U.S. are given four vaccines for polio between birth and age 6, as recommended by the Centers for Disease Control and Prevention (CDC). The CDC states that "Almost all children (99 out of 100)" who are given these recommended vaccines will be protected from the polio virus.
Since the outbreak in New York state, experts have also tested wastewater in New York's Rockland County and its neighbor, Orange County. To their consternation, the scientists found three wastewater samples that tested positive for polio — as well as four others that were genetically linked to the previously confirmed case. Because a majority of people with polio do not develop any symptoms and many polio patients merely develop flu-like symptoms rather than paralysis, this suggests that there could be other infected individuals who simply do not know that they are infected.
Given how uncommon polio is nowadays, the polio outbreak in New York comes off as particularly foreboding. Indeed, the flurry of anti-vaccination conspiracy theories that were prominent in the past two decades have spurred millions of Americans to avoid vaccinating their children or selves due to misinformation. The specter of vaccine misinformation looms over any outbreak of a near-eradicated disease.
Yet given how prominent polio vaccination is, could an epidemic really spread beyond a small region such as these two New York counties? Notably, polio vaccination rates in Rockland and Orange County are 60.34% and 58.68%, respectively. That ranks them at the very bottom: among New York's 62 counties, only one, Yates County, had a lower polio vaccination rate.
In other words, the polio outbreak very well could be related to anti-vaccination attitudes in rural Rockland County. Indeed, in addition to the possibility that the Rockland County patient contracted polio because he took an oral vaccine, Rockland County has a large Hasidic Jewish community that has sometimes harbored anti-vaccination sentiments. As The Times of Israel writes, a "fierce backlash against vaccination" exists in certain Orthodox communities, "fueled by the COVID-19 pandemic and following a measles outbreak in Rockland County in 2018 and 2019 that was centered in the area's Haredi Orthodox population."
"The risk of polio spread is limited to those who have not received the polio vaccine," Russell Medford, Chairman of the Center for Global Health Innovation, told Salon by email. "According to the CDC, in the US, almost 93% of children are vaccinated by age [two]."
Back in 2018 and 2019, a group of Hasidic Rabbis in that county experienced a measles outbreak linked to anti-vaccine tendencies in their community that precluded herd immunity; measles is preventable through vaccines. Rockland County's political leadership alluded to this last month.
"Our people defeated measles, and I'm sure we'll eliminate the latest health concern as well," County Executive Ed Daly told a news conference on July 21.
If you are concerned that these polio outbreaks could lead to a larger pandemic, health experts assure that if you received your polio vaccine in the United States, you're almost certainly safe.
"The risk of polio spread is limited to those who have not received the polio vaccine," Russell Medford, Chairman of the Center for Global Health Innovation, told Salon by email. "According to the CDC, in the US, almost 93% of children are vaccinated by age [two]."
Dr. Al Sommer, dean emeritus and professor of epidemiology at Johns Hopkins Bloomberg School of Public Health, expressed a similar view.
"It can certainly spread – infecting someone without causing illness, but being excreted by them and therefore 'passed along,'" Sommer told Salon by email. "But it would be rare for anyone vaccinated to become clinically affected even if they encountered the virus."
It is also worth noting that the polio vaccine is considered to confer durable immunity, meaning that it lasts for a long time with just the initial inoculation. This puts them in contrast with COVID-19 vaccines, which are still overwhelmingly effective but require more regular shots to keep up with new strains. This type of immunity is called transient immunity; influenza is an example of another virus for which infection or vaccination only confers transient, or short-term, immunity.
As Dr. Monica Gandhi, infectious disease doctor and professor of medicine at the University of California–San Francisco told Salon, there are two types of poliovirus vaccines, both of which work very well and provide durable immunity. "Both types of vaccine confer long-lasting immunity against the development of disease," Gandhi said.
That said, as Sommer noted, there is still reason for some caution.
"There can always be an outbreak if the virus is prevalent within a largely unvaccinated community," Sommer explained. "But, since most Americans have been fully vaccinated in the past, it has little chance of getting beyond the unvaccinated community or causing anything like COVID in the US. Given the nature of the polio virus (and its several variants), and the efficacy of polio vaccine (live and killed versions), we should not expect any epidemic or pandemic remotely like the COVID pandemic."
"Based on earlier polio outbreaks, New Yorkers should know that for every one case of paralytic polio observed, there may be hundreds of other people infected."
If another large outbreak did occur, it could be devastating. During the mid-20th century polio outbreak in the United States, tens of thousands of people were paralyzed until Dr. Jonas Salk released his polio vaccine in 1955. Even after that, however, those thousands of people lived with the ramifications of the disease for the rest of their lives — and helped pioneer the disability rights movement in the process.
This lingering memory perhaps explains why public health officials are also warning of the potential for a larger epidemic.
"Based on earlier polio outbreaks, New Yorkers should know that for every one case of paralytic polio observed, there may be hundreds of other people infected," State Health Commissioner Dr. Mary T. Bassett explained in a statement.
Bassett added, "Coupled with the latest wastewater findings, the Department is treating the single case of polio as just the tip of the iceberg of much greater potential spread. As we learn more, what we do know is clear: the danger of polio is present in New York today."
The CDC reassured the public that it is doing its best to stay on top of the potential pandemic.
"CDC continues to collaborate with the New York State Department of Health to investigate their recent polio case, including ongoing testing of wastewater samples to monitor for poliovirus and deploying a small team to New York to assist on the ground with the investigation and vaccination efforts," a CDC spokesperson told reporters on Sunday.
It is noteworthy that the sample from the infected Rockland County patient shows genetic similarity to samples found in wastewater in Jerusalem and London, Israeli and British cities respectively. This hints that the poliovirus in question did not originate in the United States, although it is not certain.
The news also raises awareness of one of the common criticisms made about the Albert Sabin vaccine, which, though usually effective, can in rare cases produce a virus that mutates, regains its virulence and cause symptomatic polio infections. Most of the world's current polio cases were caused by this vaccine, and in particular by a process which leads to the virus mutating into its more dangerous form while passing through a patient's gut.
This type of poliovirus, known as Type 2, paralyzes as few as 1 in 1,000 of the people who get it. Many others will only display symptoms like diarrhea and a runny nose and conclude that they are sick with something more innocuous.
