Updated: March 9, 2022 10:04 AM EST | Originally published: March 9, 2022 9:21 AM EST

In the fog of the war in Ukraine, it’s easy to forget about a smaller, but still very poignant tragedy that occurred months before the fighting began, back on Oct. 6, 2021. That day, a 17-month-old girl in the Rivne region in the west portion of the country was stricken with paralytic polio—19 years after the European region as a whole was declared polio-free. A second case of the disease appeared in the Zakarpattya region to the south on Dec. 24. And over those same months, 20 other children have tested positive for the poliovirus, though with sub-clinical, non-paralytic cases of the disease.

Where polio is concerned, 22 cases counts as a crisis. The disease can spread explosively and exponentially, with an average of 200 silent carriers for every paralytic case. That’s a lot of potential vectors possibly spreading a lot of virus to a lot of other people. And Ukraine—at least Ukraine as it was before the war began—did not stand still.

On Oct. 9, the Ministry of Health declared a “biological emergency on a regional scale,” and rolled out a plan in coordination with the World Health Organization (WHO) to begin inoculating 140,000 children in Rivne and Zakarpattya, ages six months to six years. On Feb. 1, 2022, the vaccination campaign got underway; just over three weeks later, it came to a halt, as the Russian invasion scattered the population and made it impossible for health workers to get safely into the field to administer the shots. Russian forces have also damaged or destroyed 34 hospitals, the Ukrainian government said Monday.

“We were hoping to bring this outbreak under control,” says Dr. Gabriele Fontana, regional Health Advisor with UNICEF, which was working along with the WHO to get the shots distributed and provide the cold chain that keeps the vaccines from spoiling. “I think we reached about 40,000 of the children we’d hoped to, but that leaves 100,000 we didn’t reach.”

Read more: Why Ukraine’s COVID-19 Problem Is Everyone’s Problem

Tragically, before the war, Ukraine was in the midst of a major transformation of its healthcare system, says Judyth Twigg, a professor at Virginia Commonwealth University specializing in global health, especially in Russia, Ukraine, and other parts of the former Soviet Union.

Back in 2016—the last time polio cases were detected in Ukraine—Twigg described Ukraine’s failure to modernize its health care system following the fall of the Soviet Union as a major cause of the resurgence of polio. Widespread corruption drove up the price of medical care and the cost of vaccines, compounded by inadequate state financing for vaccine purchases and neglect of the health care system. “Ukraine still suffered so much from that Soviet legacy with a health system that was riddled with corruption,” says Twigg. “Money that should have gone directly to the care of patients was getting diverted into the pockets of corrupt health administrators and politicians.” Meanwhile, disinformation about vaccines—some of which has been traced to Russia—drummed up widespread vaccine hesitancy.

That began to change from 2016 to 2019, during which time an American-born radiologist, Dr. Ulana Suprun, served as the acting minister of health, says Twigg. She led the country through a series of reforms, creating a new institution to transparently conduct Ukrainian health contracts; relying on international agencies for procuring drugs; and shifting patient care from hospitals to primary care offices. Suprun tells TIME that the changes to primary care were an important part of making parents more comfortable with vaccination. “For the first time ever, Ukrainians could choose a primary care physician they trust. It helped establish a better rapport between physicians and patients, and physicians were able to convince more parents to vaccinate their children,” she says.

In the aftermath of the 2015 polio outbreak, Ukraine also took aggressive action to control the disease, says Twigg. “Both the Ukrainian health authorities and the international community stepped up with an intense vaccination campaign that has gone a long way toward dealing with lack of knowledge [and] vaccine hesitancy—dealing with a lot of the misinformation about vaccines that had been keeping parents from getting their children vaccinated.” WHO data suggests these efforts paid off: while only 59% of young children, the target population for the vaccine, was vaccinated for polio in 2015, by 2019, that number was up to 83%.

The war with Russia could potentially reverse many of these gains, which were already threatened by the rise of COVID-19. As of October 2021, only 53% of one-year-olds were vaccinated for polio in Ukraine, according to the National Center for Public Health of Ukraine—suggesting that the pandemic had slowed the polio vaccination effort. Now, says Suprun, there are further “setbacks facing the health care system [that] are related directly to the destruction of facilities, the lack of medical professionals as many have joined the territorial defense or the military, and the difficulty in resupplying pharmacies and hospitals due to constant missile and other attacks by the Russian military.” Further, the displacement of citizens during the war, says Suprun, will make delivering and administering vaccines difficult.

And with the population of Ukraine now on the move—an estimated 1.3 million people have fled across the borders to neighboring Poland, Slovakia, Hungary, Romania, and Moldova—polio is moving with them.

“Even if this was not a crisis [at first],” says Dr. Siddhartha Datta, WHO’s Program Manager of Vaccine-Preventable Diseases and Immunization Division, “any population movement leads to a spread. That means that if the poliovirus finds unvaccinated children in an area it will definitely attack this population, both within the country and outside.”

Read more: ‘It’s Our Duty to Help.’ Eastern Europe Opens Its Doors and Hearts to People Fleeing Ukraine

“There are crowds of people in shelters, places of temporary residence of refugees at the borders, which cannot provide adequate sanitation and hygiene,” and the war has disrupted the supply of drinking water and food, adds Oleksandr Matskov, deputy director general of the Ministry of Health’s Public Health Center. Such conditions make it easy for polio to spread, as it is transmitted through feces, and can infect people through contaminated water or food.

Within Ukraine, the war is making health care as a whole a growing crisis—and threatening the country’s ability to treat polio or vaccinate children. Rivne Children’s Hospital—where the first paralyzed toddler was treated for polio in the fall—has so far not been directly affected by the fighting, but is getting ready for worse to come, especially as it watches hospitals in the country’s east sustaining damage from the Russian attack. Dr. Lilija Zoruk, head of the rehabilitation center, says the facility is preparing to treat the wounded, setting an evacuation plan, and watching as colleagues leave to fight for their country—all the while continuing to care for some of the country’s sickest children.

The type of polio the Ukrainian children contracted—along with the type of vaccine that WHO and UNICEF were administering—is critical to understanding the outbreak and bringing it under control. There are two types of polio vaccine: The oral polio vaccine (OPV) contains a live, weakened form of the virus. The inactivated polio vaccine (IPV)—administered by shot—contains a killed virus. Both are effective and both have their advantages—and disadvantages.

The IPV is harder and more expensive to administer, and for that reason, it is the OPV that has been used most widely over the past three and a half decades—with astonishing effect. In 1988, polio was endemic in 125 countries and paralyzed or killed as many as 350,000 children each year. A global vaccination campaign since then, led by Rotary International, the WHO, UNICEF, the Bill and Melinda Gates Foundation, and others has now run polio to ground in just two endemic countries—Pakistan and Afghanistan, where cases are now counted in the dozens.

But the OPV has a problem. On occasion, the live attenuated virus can mutate, returning to virulence, and actually cause the disease it’s intended to prevent. These cases of so-called vaccine-derived polio are rare—just three or four out of every million vaccines given, according to the Global Polio Eradication Initiative—but allowed to range free, the virus can spread as easily as the wild variety. It’s the vaccine-derived infection that struck the 22 Ukrainian children—and that virus had already done some traveling. Genetic sequencing has traced it to a form of vaccine-derived virus that first emerged in Pakistan in 2020 and then made its way through Tajikistan, before turning up in Ukraine. The 140,000 vaccines the WHO planned to administer were all the IPV variety, in order to ensure that one vaccine-derived polio outbreak would not just be replaced by another.

With the war still raging, the polio outbreak is destined to spread—though UNICEF and Ukrainian health workers are making efforts to get as many children vaccinated as possible, even with the original WHO vaccine campaign suspended. All along the refugee routes, UNICEF is setting up so-called “blue dot centers”—a reference to the organization’s blue, circular logo—to provide aid and assistance to people fleeing the war. Vaccinators, administering shots against both measles and polio, are embedded with the other health workers at the centers, in an attempt to find and protect whatever children they can.

But viruses will do what viruses do, which is to say they will take any opportunity to spread—especially in the crowded and unsanitary conditions of war. Ukrainians did not ask to be part of a major land war—and its children certainly didn’t. War is cruel; polio is cruel. Together, they are a human tragedy.

 

Correction, March 9

The original version of this article misstated the definition of vaccination coverage described in the WHO data. The vaccination coverage is for young children, not the entire population.

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Write to Jeffrey Kluger at jeffrey.kluger@time.com.

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