last drops

A trace of polio in New York sewers could help the global transition to safer vaccines

A trace of polio in New York sewers could help the global transition to safer vaccines
Photo: Dimas Ardian (Getty Images)
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The perfect infectious disease storm seems to have hit New York. Covid cases are on the rise again; monkeypox, now officially a global health emergency, is quickly reaching past containment stage; and the first case of polio in almost a decade was detected in New York City suburbs late last week.

It was the very rare case of vaccine-derived polio. That typically happens when an unvaccinated person comes in close contact with the stools or respiratory secretions of someone who recently received the oral polio vaccine. Those vaccine drops contain an attenuated version of the virus.

Oral polio vaccines haven’t been used in the US since 2000. Instead injectable vaccines containing inactive virus are used, carrying no risk of causing vaccine-derived infections.

The New York patient, an unvaccinated man in Rockland County, developed permanent paralysis, and initial investigations suggest he didn’t contract the virus outside the US. This likely means that the virus was imported into the country by someone else, and that other cases might have gone undetected, as only a small percentage of all polio cases develop paralysis.

What is vaccine-derived polio?

It’s concerning—not for the overall population, but for the 7% who don’t have full three-dose coverage of polio vaccines, and are therefore susceptible to contracting the disease. Rockland county is at particularly high risk. It’s a community with extremely low vaccination rates. Only 61% of the population has received the three doses of polio vaccine, according to the New York health department.

The county’s low vaccination rate isn’t exclusive to polio. Two years ago, low measles immunization rates led to an outbreak so prolonged it nearly cost the US its measles-free status from the World Health Organization.

Cases of vaccine-derived polio are extremely rare—less than one every 2 million vaccine doses—but they do occur where immunization is still done with oral vaccines, such as African countries. When they are identified, the control protocol involves contact-tracing to identify people potentially exposed, then ensuring those people and their immediate community are up to date with their vaccination. “A silver lining here is that you are going into a community that is very vaccine resistant, and you could use this moment to vaccinate children,” says Stephen Morrison, who directs the Global Health Policy Center at the Center for Strategic and International Studies, a US-based bipartisan think tank.

But there is another potential silver lining that could prove even more important: the New York case could provide renewed funding for the global eradication of polio, and the switch to the injected vaccines, speeding up the phasing out of oral ones.

Polio anywhere is a threat everywhere

“Hopefully, this is a teachable moment,” says Morrison. It’s easy to forget the urgency of eradicating polio when it’s something that happens in faraway corners of the world, but when the virus emerges close to home—in New York, or in London’s sewage (as it happened a few weeks ago)—it reminds us that any setback experienced in the vaccination and eradication campaigns can be felt globally.

In order to eradicate the wild virus, the oral vaccine is used first. Once the cases reach zero in a particular area, the routine campaign can switch to injected vaccines. Polio is only endemic in two countries, Pakistan and Afghanistan, but oral vaccines are used for routine immunizations in many places, because of the cost of switching to injected vaccines, as well as a shortage of them.

“We have gotten down to vanishingly small numbers of wild cases, but they are in terribly difficult environments to reach. It is a long and expensive proposition to get them, and tough to accomplish, but what’s the choice?” he says.

The progress made in polio eradication in recent years is close to a global health miracle. In 1988, three strands of the virus were endemic in 125 countries, and 350,000 cases were registered every year. Currently, only one strand remains endemic, while two have been eradicated completely. There are only 175 cases in two countries, and the target is for the world to be polio-free by 2026 (the previous target, set for 2023, was missed because of covid-19 pandemic setbacks). The plan, developed by the Global Polio Eradication Initiative (GPEI), a coalition of governments, international organizations and public health philanthropies, comes with a $4.8 billion price tag, or about $1 billion per year.

The price tag of polio eradication

Meeting the 2026 deadline would make it possible to retire oral vaccines shortly after 2030 (pdf, p. 26) from Pakistan and Afghanistan. In most other parts of the world, where polio has been eradicated for several years, the switch to injected vaccines could happen much faster. “The global switch campaign is going on, but it’s expensive, and slow,” says Morrison.

Cost is a serious challenge. Oral vaccines cost between $0.12 to $0.18 per course, while the injectable ones are up to 30 times more expensive, ranging between $1.00 to $3.28. That doesn’t include the costs of syringes, needles, training, and safe needle disposal need to administer the injected version. And there is an issue of availability: Less than a third of the doses that would be needed to switch to injected vaccines are actually available.

The higher cost can be prohibitive for poor countries, but still pale in comparison to the public health burden of treating potential vaccine-derived cases, which can cause lifelong paralysis. The risk of such cases is higher as vaccine-hesitancy increases around the world. Investing in polio eradication, alongside a switch to inactivated virus vaccines, is an investment that could solve both issues, and justifies a significant investment from rich countries.

If the eradication campaign is successful, an estimated $33 billion will be saved by 2100. Yet mobilizing rich countries’ to invest in vaccines for diseases that seem far gone isn’t always easy. Without continued focus polio could become yet another global health issue stuck in its perpetual cycle of crisis, followed by complacency, followed by new crisis.

As the GPEI seeks support and funding for the final leg of the eradication program, cases such as the one that emerged in New York can drive home the importance of global polio eradication efforts even in the face of threats like a global recession and the ongoing cost of the covid pandemic. “We’ve gotta care about what happens globally, because it is going to spill into our backyard,” Morrison says.