Thirty years ago, the world united under a bold promise: a future free from polio.

In the decades since, organizations from across the world have worked alongside dedicated governments and health workers to make good on that promise. In addition to developments like improved access to clean water, vaccination efforts like those led by the Global Polio Eradication Initiative have yielded an incredible drop in wild poliovirus cases: from 1,000 a day in 1988, to 22 in all of 2017. If we finish the job, polio will become only the second human disease, after smallpox, to be wiped from the face of the earth.

But the road to eradication has been longer and harder than expected. While last year saw a record-low number of wild polio cases, we have fallen short of stopping the disease completely. One child affected is too many, and so far this year there have been 20 children paralyzed by wild poliovirus.

At the same time, there have been outbreaks of vaccine-derived polio, which occurs­ in rare instances when the weakened virus in the oral vaccine mutates to virulence, and can spread easily in large, unvaccinated populations. These outbreaks have occurred in high-risk countries like the Democratic Republic of Congo, Papua New Guinea, Somalia and Niger, and indicate that we are failing to reach enough children.

No matter the setting or viral strain, these challenges share a common cause: barriers to reaching every child. In Afghanistan, for example, nomadic populations, cross-border movement, insecurity and difficult terrain mean that many vulnerable communities remain inaccessible to polio vaccinators.

Though where we do gain access, the impact has been profound. In Pakistan and Nigeria — which, along with Afghanistan, make up the world’s three final polio-endemic countries, down from 125 countries in 1988 — we are steadily reaching more children and the number of polio cases is dwindling, showing what is possible when we gain new ground.

For the children and families affected, contracting polio is a tragedy. For us, every new case is also a lesson — pointing to where we need to intensify our efforts and reminding us how quickly polio can come surging back if we aren’t vigilant.

For every paralyzed child, there are an estimated 200 others who carry the virus without any symptoms. This is why, even as the world sees just a handful of cases, we must reach millions of children each year to prevent a massive resurgence of polio. If these vaccination efforts ceased, the consequences would be catastrophic. Within 10 years, polio could be back on every family’s doorstep, paralyzing as many as 200,000 children each year.

We understand that delivering vaccines is no simple task. Polio has taken refuge in some of the most complex and dynamic environments in the world. But over time we’ve learned how to deliver health services in the face of extreme adversity, even in areas with almost no infrastructure.

We proved this in 2016, when the virus resurfaced in Nigeria after two years without a case. A critical front in the response was Lake Chad, a massive body of water that borders Nigeria, Chad, Cameroon and Niger. Health workers painstakingly mapped the many islands that dot the lake and traveled hours by canoe, reaching hundreds of settlements for the first time. Solar-powered refrigerators they brought along kept the vaccines cool.

Today, there are still parts of Nigeria where we can’t reach children or properly track the virus, due to a combination of inadequate infrastructure, population movements and insecurity. But while we remain cautious, we have yet to see another case of wild polio since the 2016 outbreak.

Our partnership has also demonstrated its capacity to operate strategically, despite insecurity. Last year in Syria, after conflict led to blockades that prevented health workers being able to reach cities, we responded quickly and effectively to an outbreak of vaccine-derived polio. We vaccinated fleeing children at transit centers and camps, and we partnered with local authorities to quickly administer vaccines during windows of safety — strategies we have used in conflict zones worldwide. As a result, Syria has seen a year without another child paralyzed.

We have also worked globally to strengthen local health systems and respond to community needs beyond polio vaccination. In Karachi, for example, Rotary International is working with local partners to install water-filtration systems in at-risk communities. Similar projects — including delivering bed nets, nutrition supplements and vaccines against measles, meningitis and tetanus — go on every day, anywhere that we fight polio. And this infrastructure will not disappear with the last poliovirus, but can be repurposed to fight other diseases and accelerate progress toward ambitious global goals like universal health coverage long after polio is eradicated.

These examples illustrate the tenacity of this coalition, which — thanks to committed vaccinators, donors and advocates around the world — has come so far since making that promise in 1988 to rid the world of polio. We are so close to keeping that promise. We have seen how readily the virus can push back, but we are more committed than ever before.

There will be a livestream for Rotary’s 2018 World Polio Day Event on Oct. 24, at endpolio.org.

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