This also marks World Immunization Week, a coordinated effort to make sure that people everywhere understand the importance of getting immunized to protect against vaccine-preventable diseases.

At the time, Nigeria had done an amazing job tackling polio—reducing reported cases by 95 percent in just one year. But it was still circulating in six Nigerian states. While 95 percent might seem like success, as long as a single child remains infected, children across Africa and around the world are at risk.

Thanks to the effort of so many, Nigeria’s Borno State is now the only place in Africa today where polio is still circulating. It will take ingenuity to end polio there, and it will take persistence to continue reaching children in the surrounding area with vaccines to protect them from the disease until it is eradicated. But we’re confident it can be done. And when that happens, Africa will celebrate one of the biggest victories ever in public health.

Since our first meeting in 2010, the two of us have worked together on a range of other projects to help improve health in Nigeria and across Africa. We supported the establishment of emergency operations centers in Nigeria and other countries to keep polio from spreading. This turned out to be a blessing during the 2014 Ebola outbreak in West Africa. When the disease first appeared in Nigeria—an international travel hub that is home to more than 180 million people—the staff of an emergency operations center set up in Lagos jumped into action and stopped the disease in its tracks. It’s almost unimaginable to think what would have happened without them.

In the state of Kano, we are working with the government to ensure that children can get essential childhood immunizations against tetanus, pneumonia, liver cancer and measles. And when parents bring their children into a clinic for vaccinations, health workers can address other health issues, too, like nutrition, care for pregnant mothers and newborns and malaria prevention and treatment. We have since widened the program to several other states.

Vaccines are also one of the best tools to save lives in an epidemic, such as the meningitis C outbreak happening now in Nigeria and other West African countries. And because of the devastating impact malnutrition has on Nigeria’s children – leading to 300,000 deaths annually and causing stunted growth and development in millions more – we have expanded our partnership to include nutrition programs across 12 states.

Earlier this year, we also helped launch the End Malaria Council, a group of influential public and private sector leaders committed to ensuring that malaria eradication remains a top global priority.