How Polio Returned to the United States
It was a jolt, to be sure. The country was declared polio-free
in 2003.
But at least no one had turned up sick. The proof came from routine tests of sewage samples, which can alert health officials that a virus is circulating and allow them to intervene quickly.
Based on genetic analysis
of those samples, officials in the United Kingdom moved to protect the city’s
children by reaching out to families with kids under 5 who hadn’t been fully
vaccinated.
Polio’s first appearance in almost a decade in the U.S., confirmed in late July by health
officials in New York, would play out quite differently.
In the U.S., public health agencies generally don’t test sewage
for polio. Instead, they wait for people to show up sick in doctor’s offices or
hospitals — a reactive strategy that can give this stealthy virus more time to
circulate silently through the community before it is detected.
In New York, the first sign of trouble surfaced when a young man
in Rockland County sought medical treatment for weakness and paralysis in June.
By the time tests confirmed he had polio, nearly a month had passed.
Because the majority of polio infections cause no symptoms, by
the time there’s a case of paralysis, 100 to 1,000 infections may have
occurred, said Dr. Yvonne Maldonado, a professor of pediatrics at the Stanford
School of Medicine who chairs the American Academy of Pediatrics’ committee on
infectious diseases.
“You’re already chasing your tail if you’re going to wait for a case to show up,” she said.
Only after the case was identified did New York health officials start the sort of surveillance the British did, testing wastewater samples from Rockland County and beyond to help determine if the virus is spreading and where. Like many parts of the U.S., New York already was collecting sewage and analyzing it to track the spread of COVID-19.
Health officials say they’re now
testing stored samples for signs of polio. They say they’ve detected polio in a
few Rockland County samples but need to analyze more to understand what the
initial results represent.
For decades, the cost of doing wastewater surveillance for
diseases like polio pretty clearly outweighed the benefit.
High U.S. vaccination rates, topping 90 percent, made the risk of such diseases incredibly low, though there have long been pockets of population in which rates are far lower. Rockland County, a suburban area northwest of New York City, is one such place.
It suffered an extended outbreak of measles, another
vaccine-preventable disease, in 2018 and 2019 that was largely concentrated in
its Orthodox Jewish community, where many opt out of vaccines. Several news
organizations have reported that the polio patient is a
member of that community.
Nationally and globally, there are signs that the pandemic has opened up new vulnerabilities to diseases long in retreat. Routine immunizations have been hindered by a host of obstacles, including COVID-19-related lockdowns and growing vaccine resistance stoked by misinformation and politicization.
A recent analysis by UNICEF and the World
Health Organization showed that the percentage of children worldwide who
received all three doses of the vaccine against diphtheria, tetanus and
pertussis — a measure of overall immunization — dropped 5 points between 2019
and 2021 and that measles and polio vaccinations fell, too. The organizations
say that’s the largest sustained decline in childhood vaccinations in the
roughly 30 years they’ve been collecting data.
That could create greater risk of polio, a scourge of the first
half of the 20th century in the U.S. Highly contagious and potentially
life-threatening, polio historically has victimized mostly young children,
attacking their spinal cords, brain stems, or both.
The virus spreads when fecal material or respiratory droplets
from infected people get into water or food or onto other people’s hands, which
they then put into their mouths. This may sound unusual, but it’s among the
more common ways viruses circulate, especially among children.
Around 70 percent of those who are infected show no signs of the
illness but can infect others. Of those who do get sick, most have mild
symptoms, such as fever, sore throat, muscle weakness, and nausea. But about 5
in 1,000 infected people develop irreversible paralysis.
At its peak in 1952, polio killed more than 3,000 Americans and
paralyzed more than 20,000. Images of children encased in coffin-like iron
lungs terrified parents. Those fears faded swiftly after the first polio
vaccine was approved in 1955. Within two years, cases dropped by as much as 90
percent.
Since 1988, when the Global Polio Eradication Initiative began
pouring billions into immunization campaigns and surveillance around the world,
polio has been eradicated in much of the rest of the world. Wild polio, the
kind that occurs naturally, remains endemic in just two countries, Pakistan,
and Afghanistan.
But there’s another kind of polio that’s circulating, one linked
to the type of vaccine that’s used in much of the world, particularly
lower-income countries. This oral vaccine, which hasn’t been used in the U.S.
since 2000, is easy to administer — just a few drops on the tongue — and cheap
to make. It uses weakened live viruses to trigger the immune system to create
protective antibodies.
That brings a bonus. When the vaccinated shed the weakened live
viruses in their stool, they can spread to the unvaccinated, triggering
protective antibodies in them as well.
But it also brings a risk. In rare instances, when the weakened
viruses circulate in people who have not had the vaccine or are
under-immunized, they revert to a form that can sicken unvaccinated people,
causing the disease they were meant to prevent. The injectable polio vaccine
used in the U.S. contains only inactivated viruses and cannot cause this.
Cases of vaccine-derived polio have surged in recent years after
global health authorities in 2016 decided to remove one strain of polio
from the oral vaccine after determining that the wild version had been
eradicated globally. That left a growing number of children with no immunity to the vaccine-derived
version of that strain, Type 2. (The injectable form of vaccine used in the
U.S. conveys protection against all strains of polio.)
Type 2 vaccine-derived poliovirus is the kind that was found in
the British sewage samples. It was also the kind that infected the unvaccinated
Rockland County man, indicating a transmission chain from someone who received
the oral polio vaccine, health officials in New York said.
Officials are still investigating where the man caught the
virus, here or abroad. The Washington Post has reported that the man traveled to Poland
and Hungary this year, but a spokesperson for the Rockland County Health
Department said in an email, “The person did not travel outside the country
during what would have been the incubation window.”
Ultimately, New York health officials will use wastewater
monitoring to tell them quickly whether they have a bigger problem, essentially
allowing them to test thousands of people at once for polio infection rather
than individually, David Larsen, an epidemiologist and Syracuse University
professor who directs the state’s wastewater surveillance network, said in an
email.
Wastewater testing for polio has been a staple in developing
nations for decades, but at least a few countries where cases are rare and
vaccination rates are high do it, too.
The U.K. began monitoring wastewater in 2016 for polio and
several other viruses that occur in the gastrointestinal tract, a spokesperson
for the British health security agency said via email. (It has since added the
virus that causes COVID-19 to the list.)
Israel has monitored sewage for polio since 1989. In 2013,
health officials were able to detect an outbreak of wild polio just from
sampling and launch a vaccine campaign in response without ever experiencing a
case of paralysis. This year, though, a young child in the Jerusalem area came
down with paralytic polio. Public health authorities there found additional
infections through sewage tests.
Some U.S. public health officials have been skeptical of the
value of such testing here.
“I’ve always been unenthusiastic about doing it for polio in the
U.S. and a big supporter of doing it elsewhere, where there are deficiencies in
other surveillance systems,” said Mark Pallansch, who retired in 2021 after
spending much of his career working on polio eradication efforts for the
Centers for Disease Control and Prevention.
COVID-19 has triggered a blast of interest in wastewater
surveillance, prompting cities, states, and colleges to launch programs and
opening a floodgate of funding for them.
The CDC sent federal money to health departments in over 40
jurisdictions to support such tracking efforts, working with them to collect
data that’s published on the agency’s National Wastewater Surveillance System
website. A spokesperson said in an email that the agency was working to expand
the platform to include data on other pathogens, from foodborne infections like
salmonella to influenza, but not polio. Testing nationally for polio would be
labor and resource intensive, requiring increases in public health laboratory
capacity, the spokesperson said.
One asset of wastewater monitoring is the ability to pivot
quickly to test something new.
In November 2020, the Sewer Coronavirus Alert Network, based out
of Stanford and Emory universities, started daily monitoring at California
wastewater plants for the virus that causes COVID-19. It’s since added
monitoring for other pathogens, including COVID-19 variants, the common
respiratory virus RSV and, most recently, monkeypox. Such additions are
relatively economical since the network can test for multiple pathogens from a
single sample, said Marlene Wolfe, one of the two principal investigators and
an assistant professor at the Rollins School of Public Health at Emory.
In adding more tests, Wolfe said, the question is always whether
monitoring a disease this way is likely to surface anything of enough concern
to drive public health decisions.
Many question whether the expansion of wastewater testing fueled
by the pandemic will last. Maldonado, the American Academy of Pediatrics’
infectious diseases committee chair, said the recent polio case is another signal
that more disease tracking is critical.
“Maybe this is a clarion call for us to really start building
better surveillance networks,” she said.
Robin Fields is a reporter with ProPublica. She joined
ProPublica as a reporter in 2008, became a senior editor in 2010 and was later
promoted to managing editor in 2013 prior to returning to the reporter role.
ProPublica is a Pulitzer Prize-winning investigative newsroom.
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