According to Dr. Wenger, there are only 12 known cases of the wild poliovirus in existence today, in just two countries: Afghanistan and Pakistan. "In the last couple of years, we've seen unprecedented progress. In 2015 we could only find 74 cases; in 2016 we found 37, and then this year so far we've found only 12 in only two countries."

The reason: a mass immunization effort to orally vaccinate 2.5 billion children in 122 countries, bolstered by the 1988 launch of the Global Polio Eradication Initiative.

Although Dr. Jonas Salk is credited with developing the first safe and effective oral polio vaccine in 1955, there were still about 350,000 cases of polio worldwide 30 years later. "In a lot of places, children don't always get all the vaccines that they are supposed to, and that's a chronic problem, said Dr. Wenger.

The virus can only live in people, he says, and it needs new people to infect to keep on spreading and keep on living. "If you make all those people in an area immune, then the virus can''t find new people to infect. So if we can get enough children in an area vaccinated, the virus dies off."

Since the World Health Assembly's 1988 launch of the Global Polio Eradication Initiative, the number of cases has been reduced by 99.9 percent, saving more than 13 million children from paralysis. Economic modeling has found that the eradication of polio would save at least $40 billion to $50 billion between 1988 and 2035, mostly in low-income countries.

Bill Gates is hopeful the disease will become the second disease after smallpox to disappear for good. "Progress in fighting polio might be one of the world's best-kept secrets in global health," he acknowledged in the foundation's 2017 annual letter. But soon, he hopes, it will be a secret no more. "If things stay stable in the conflicted areas, humanity will see its last case of polio this year."

The heroes behind the mass vaccination campaign

Caused by a virus, polio is a highly infectious disease, spread from person to person, that invades the nervous system and can cause paralysis in a matter of hours. Among those paralyzed, 5 percent to 10 percent die when their breathing muscles become immobilized.

The first initiative to wipe out polio through mass vaccination of children began in 1985 with the launch of PolioPlus by Rotary International. The first and largest internationally coordinated private-sector support of a public health initiative, PolioPlus had an initial fundraising target of $120 million and a goal of vaccinating all of the world's children by 2005.

Later, in 1988, the Global Polio Eradication Initiative was formed, led by national governments and four partners: Rotary International, the World Health Organization, Unicef and the Centers for Disease Control and Prevention. In 2007 the Bill and Melinda Gates Foundation joined in as a major supporter of GPEI. To date the foundation has contributed nearly $3 billion in the push to end polio, says Rachel Lonsdale, a spokeswoman for the Gates Foundation.

"World Polio Day is a day that has been set aside to celebrate all of the workers that are involved in this," says Wenger. "It is really a global effort to get to zero. There are hundreds of thousands of ground-level health workers all over the world trying to help kids have a better life. Those are the people you don't hear a lot about, because they are at the bottom end of the vaccination distribution chain. But they are actually the most important."

According to Wenger, there are a number of issues, including political and social turmoil, that have made vaccinations in some areas of the world difficult.

"Immunizing children in conflicted areas is hard — and dangerous," said Melinda Gates in the Gates Foundation 2017 report. In North Waziristan, Taliban factions forbade immunizations, and there have been reports of the murders of vaccination teams in Africa. According to the United Nations Children's Fund, Syria had a 90 percent vaccination rate, but after civil war began in 2011, it fell rapidly in wartorn areas.

Although GPEI is at the final stages of polio eradication, the Gates Foundation and Rotary International renewed its longstanding fight by announcing a commitment of up to $450 million in June to support the ongoing struggle to end polio. Not until it's certain that polio has been completely wiped out will the commitment end, says Dr. Wenger.

"You might be wondering why we're spending so much money when there's only 12 cases," he says. "We want to be sure we finish it off."

"What we don't want is cases moving into places like the Central African Republic, South Sudan and Ukraine," said Rebecca M. Martin, director of global immunization for the Centers for Disease Control and Prevention.

According to the World Health Organization, as long as a single child remains infected, children in all countries are at risk of contracting polio. Failure to eradicate polio from these last remaining strongholds could result in as many as 200, 000 new cases every year, within 10 years, all over the world.

What began 62 years ago in Dr. Salk's University of Pittsburgh laboratory and later implemented by Bill Gates and others has been one of the great medical achievements of our time. Coincidentally, Jonas Salk and Bill Gates have something more in common: Both share the same birth date — October 28.

CNBC is a USA TODAY content partner offering financial news and commentary. Its content is produced independently of USA TODAY.