People often ask me how I know the world is getting better. I usually point to numbers like this one: Because of efforts to eradicate polio by groups like Rotary International, more than 16 million people are walking today who would otherwise have been paralyzed.

That’s more than 16 million people who can walk to school. More than 16 million people who are better able to start a business or carry their child to bed. More than 16 million people who are living better lives, because a group of health care workers, volunteers, government leaders, and funders devoted themselves to fighting polio.

Rotary International is one of the key players in this global coalition. For more than 30 years, their volunteers have traveled to some of the most remote, most dangerous parts of the world to administer vaccines to children. Their members have donated their time and resources to keep eradication on the global agenda. They are part of the reason why we are breathtakingly close to wiping polio off the map for good.

At their annual convention in Atlanta, I encouraged more than 25,000 Rotarians to keep fighting. We’ve gone from 40 cases an hour back in 1988 to just 40 cases in all of 2016. But if we stop now and don’t get to zero, experts say that within a decade there would be 200,000 new cases of polio every year.

We’re closer now than we have ever been to eradication. If groups like Rotary keep going, no person will ever have to suffer from polio again.

Here is the text of my remarks:

It’s great to be here today and I’m excited about continuing to support Rotary’s fantastic work on polio. The $450 million I just mentioned will bring the total amount raised by our partnership since 2007 to nearly $1.5 billion. That’s just amazing. But money is only one piece of the story of Rotary’s leadership on polio eradication.

In fact, polio eradication began with Rotary more than 30 years ago. And since then, in the face of challenges nobody could have predicted, you have kept it on the global agenda. In Washington D.C. and European capitals, Rotarians have insisted that the fight against polio gets the funding it deserves. In high-risk countries, Rotarians have made sure that government leaders—at all levels—are doing the right thing.

And, of course, Rotarians have volunteered. Ann Lee Hussey, who was diagnosed with polio as a toddler, has led volunteers on over 25 trips to some of the most dangerous places on earth. Dr. Yoshi Sekiba, a Japanese pediatrician, just led a team of 60 Rotarians to Delhi—for the 16th consecutive year. And thousands of Rotarians in at-risk and endemic countries have spent countless hours immunizing kids.

Rotary also has done something that no other organization could do. It has mobilized members to build bridges when we needed them most. I’m thinking of people like Marie-Irene Richmond-Ahoua, who lives in Ivory Coast. When there was a coup in her country years ago, the new military ruler cancelled a National Immunization Day. She appealed, saying children should not suffer because of a conflict created by adults. And days later, the general presided over the opening of the rescheduled immunization day.

In Pakistan, Rotarians have helped overcome mistrust by working with Islamic scholars and religious leaders—who are now advocates for the polio program.

And Rotary has funded dozens of community centers and immunization posts in high-risk areas. For example, a Rotary-funded health center run by Tayyaba Gul—a member of the Rotary Club of Islamabad—is working with displaced people to help them understand that polio immunization is a normal part of postnatal care. These efforts have helped reduce polio in Pakistan from 306 cases in 2014 to just two cases so far this year.

This kind of tactical approach is what’s needed to finish the job on polio. But it’s important that we not lose sight of the massive effort that has brought us to this point. The Global Polio Eradication Initiative is the single most ambitious public health effort the world has ever undertaken.

We have gone from 125 endemic countries in 1988 to just three endemic countries today . . . and from 40 cases an hour thirty years ago . . . to less than 40 cases in all of 2016.

It’s easy to forget how terrible a disease polio was, and how far we have come. So, let’s take a moment to reflect on the progress. Not all that long ago, polio was everywhere. In 1994, the Americas were certified as polio-free. In 2000, the Western Pacific region was certified as polio free. In 2002, Europe was certified as polio-free. In 2014, Southeast Asia—including India—was certified as polio-free. This year, we are down to just a handful of cases in three countries: Pakistan, Nigeria, and Afghanistan.

The scale of this effort is phenomenal. Since the year 2000, more than 10 billion doses of oral polio vaccine have been administered by an army of 20 million volunteers and a global team of thousands of frontline health workers.

But in my opinion, the statistic that captures the impact the best is this one: more than 16 million people are walking today who would otherwise have been paralyzed by polio.

Yet, I know there is one question on your minds. It is on my mind all the time. Why has it taken so long? The original plan was to be done with polio by 2000—before I was even involved. And polio has been my top priority for a decade now. I think we’d all agree this has been harder than any of us expected.

The answer has to do with the ambition of the polio eradication program. Eradication means zero cases. All 7.5 billion people on the planet. Across all 200 million square miles. No polio.

That includes areas where there is war. It includes countries where public health systems are virtually non-existent. It means reaching children in the most inaccessible places on earth—not just once but many times to ensure they’re protected.

What worked in over 100 countries where elimination was achieved years ago wasn’t enough in the last handful of countries.

But that is what’s so impressive about the polio program. Through persistence and innovation, it has risen to the challenge, again and again. It is this talent for generating new ideas, building on lessons learned, and adapting to new circumstances that makes me optimistic we will get to zero. Let me share a few brief examples of what I mean.

One of the toughest things to do is reach all the children who need the polio vaccine. This is especially hard in conflict areas because it is so difficult to build trust with all sides. Yet, in Afghanistan—despite its enormous security challenges—most of the country remains polio free. Why? Because the people running the program there have helped build understanding that the only way to get rid of polio is to rise above political, religious, and social divisions.

Working in areas of instability is extraordinarily challenging, and frontline health workers have risked – and in some instances sacrificed – their lives. And as quickly as progress is made, it can disappear. The detection of polio in Nigeria last year—after a gap of two years—was a reminder of how hard it is to eliminate the disease in conflict areas. Fortunately, the Nigerian government responded swiftly.

Another challenge is that some parents refuse to have their children immunized because of fear or misunderstanding. In Nigeria and Afghanistan—as in Pakistan—efforts to engage traditional and religious leaders have made a big difference. Today, the overwhelming percentage of parents in these communities wants their kids to be vaccinated.

One of the people who has helped with this is His Highness, the Emir of Kano, one of Northern Nigeria’s most prominent traditional leaders. He once ventured into an area known for its resistance to polio vaccination and consumed an entire vial of vaccine to reassure people that it was safe.

The hiring of thousands of female health workers and social mobilizers also has helped build trust with families in traditional societies where men cannot enter other people’s homes or interact with mothers.

Five days a week, Fiaz Bibi, a vaccinator in the Punjab province of Pakistan, covers herself with a burqa, walks three miles to a dispensary to pick up supplies, and then makes her rounds among the 105 families in her community. Temperatures can exceed 110 degrees, and Fiaz often feels the disapproving eyes of villagers following her. Yet, she persists—visiting every nook and cranny of her village—because she believes it is her “moral duty” to make sure every child is protected against polio.

Another challenge in getting to zero is knowing where the children are who need to be vaccinated. In the last few years, the polio campaign has made great progress on this, thanks in part to something we take for granted in wealthy countries . . . maps.

Maps that vaccinators in northern Nigeria used until a few years ago were hand-drawn, inaccurate, and incomplete. It is estimated that thousands of small hamlets were never included in the vaccination program’s plan because—simply put—they weren’t on the map. You can’t beat polio that way.

Today, the maps identify previously missed villages. And with more accurate information about the location and size of these communities, the maps help supervisors manage their teams efficiently.

Another big challenge is finding the last vestiges of the virus. With fewer and fewer cases of polio, this work is both more difficult and more important. To stop the virus completely, we have to know where it is still hiding.

There are two ways to do this. The first is by looking for paralyzed children and testing their stools to see if they have polio. This is a massive undertaking, supported by a network of 146 laboratories around the world. They test 200,000 samples every year and 99.9% of the time, the results come back negative. But the tiny fraction of positive results tells public health officials where to focus to prevent polio from spreading.

The other way we know where polio is circulating is to look for it in sewage systems, especially in high-risk areas. This can identify polio in the environment before it has a chance to paralyze a single child. In Nigeria, Afghanistan and Pakistan alone, there are more than 125 environmental detection sites operating. And worldwide, over 70 countries are doing environmental surveillance to help make sure that if the virus crosses borders, it will be found and stopped.

These types of innovations are what it will take to reach the goal of eradication. Every example I just gave also has the potential to boost other global health efforts. Better maps will help health workers reach children with other life-saving vaccines and medicines. The surveillance networks will help detect and prevent the spread of other infectious diseases like Ebola, measles, and yellow fever. And a huge cadre of trained health workers, armed with vital data, now have the expertise to provide critical health services to the most vulnerable people.

The most recent Ebola outbreak in West Africa is a case in point. Tragically, that outbreak killed more than 11,000 people, mainly in three countries—Guinea, Liberia, and Sierra Leone. 

But the death toll would have been much greater if quick action by polio workers hadn’t stopped the disease from spreading in neighboring Nigeria. As soon as they realized that a few cases had spread to Lagos—Nigeria’s largest city—the polio workers jumped into action.

They set up an emergency operations center to coordinate efforts. They tracked hundreds of people who had come in contact with Ebola patients. And they deployed community volunteers to get out the message on how to stay safe.

Their efforts prevented what could have been an even greater tragedy if Ebola cases had been allowed to multiply over and over in Nigeria—an international travel hub with a population nearly eight times the size of the three affected countries.

This is what is so exciting about Rotary’s 30-year fight. Not only are you eradicating one of the worst diseases in history. You also are helping the poorest countries provide their citizens with better health and a better future. And getting to zero is incredibly inspiring as an achievement of humanity.

Some people, especially these days, think the world is getting worse. The progress on polio is a reminder of what people can accomplish when they are bold, determined, and willing to work together.

Earlier this morning, representatives from donor countries pledged to support the final push on polio. It was great to see Canada, Japan, Germany, Australia, the European Commission—and His Highness Sheikh Mohamed bin Zayed from the United Arab Emirates—stepping up with new pledges. I’d also like to acknowledge the United States—the largest government funder of the Global Polio Eradication Initiative.

Their support and the support of other donor countries is an example of why foreign aid is so important. Without it, we wouldn’t have come as far as we have on polio. And we wouldn’t have made such great progress reducing child deaths from other preventable diseases like pneumonia, diarrhea, and malaria.

My favorite chart shows that in the last 25 years, the world has cut childhood deaths in half. If you add it all up—from 1990 to 2015—that is 122 million lives saved.

We could cut childhood deaths in half again by 2030 if governments continue to invest in things like vaccines, maternal and newborn health, and HIV prevention and treatment.

This is what breaks the relentless cycle of disease and poverty in low-income countries. And that is what enables countries to prosper.

Yet, some in Washington D.C. are talking about deep cuts to foreign aid. These investments amount to less than 1 percent of the U.S. budget, so eliminating them wouldn’t make a dent. But continuing these programs will make a big difference in the lives of millions of children and families around the world.

Helping other countries fight poverty and disease makes the world more stable, and it makes Americans and people everywhere safer. Foreign aid delivers a fantastic return on investment. You know this, because you have been following the success of the polio campaign for years.

When the story of polio eradication is written, it will be about millions of individuals linking arms and persevering in the face of innumerable setbacks. Rotary laid the foundation with its unwavering sense of purpose and its belief that anything is possible if you put your mind and body to it.

But we aren’t quite ready to write that story yet. To be certain that polio is eliminated, we have to maintain vaccination rates at a very high level. And even when we get to zero, we have to go three years without a single new case.

There is no other option, because if we fail, polio will return to the countries where it has been eliminated—and it will kill or paralyze hundreds of thousands of children a year.

So, it is critical that Rotarians continue to stay engaged. The money you contribute pays for the day-to-day costs of the eradication effort. Your volunteer efforts are ensuring that vaccines are reaching the children who need them. And as the most important advocates for polio eradication, no one can do a better job of reminding government leaders that this work is important and not yet finished.

By almost any measure, the world is getting better for humanity. People are living longer, healthier lives. Extreme poverty is below 10 percent. We eradicated smallpox. These are astonishing achievements, and when we add the end of polio to the list—which I’m certain we will—it will be another triumph for humankind.

It also will be a testament to the compassion, generosity, and kindness of more than a million Rotarians around the world. You are the people who are making it possible to get to zero. And that will be something worth celebrating. Thank you.