In his 2013 State of the Union address, President Obama made a strong commitment to help save the world’s children from preventable deaths. His was not an empty promise.

The commitment followed a U.S.-organized summit called the “Child Survival: Call to Action,” which focused the world’s attention on ending preventable maternal, newborn and child death. In the course of just two years, there has been remarkable progress in saving the lives and improving the health of tens of millions of children and mothers.

This has helped drive forward a remarkable trend in global health.

Since 1990, under-five mortality has been nearly halved – from 12.6 million to 6.6 million – while maternal deaths fell by nearly 50 percent, from 543,000 to 289,000.

This is an historic achievement, thanks largely to innovative partnerships, including many supported by the U.S. government. The fact that this has occurred concurrently with significant increases in global immunization coverage in poor countries is no coincidence. Worldwide, 83 percent of children now receive routine immunization, such as a full course of diphtheria-tetanus-pertussis (DTP) vaccines, up from about 60 percent in the early 1990s.

Instrumental in this story has been the GAVI Alliance, whose members include UNICEF, the World Health Organization, the World Bank, the Bill & Melinda Gates Foundation, donor countries – including the United States – implementing countries, the private sector and civil society. Since its inception in 2000, the Alliance has helped immunize 440 million children, increasing the coverage of routine immunization but also providing access to newer vaccines that target the two largest killers of children, pneumonia and diarrhoea, and even two causes of cancer. This is equivalent to the combined populations of the United States, Canada, the UK and Australia. As a result around 6 million lives will have been saved, or more than the number of children born in those countries, each year.

While we have made great progress together, there still is a long way to go.

That is what is so important about this week’s U.S.-hosted event, Acting on the Call: Ending Preventable Child and Maternal Deaths, under leadership of USAID Administrator Rajiv Shah and the governments of India and Ethiopia.

One month after the GAVI Alliance outlined the opportunity – and resources required – to significantly accelerate access to life-saving vaccines and expand immunization coverage to the world’s most vulnerable people in 2016-20, Acting on the Call represents a critical moment in this effort. It is an opportunity to dramatically improveprogress against the leading killers of children and women, including through expanded use of vaccines, one of the most cost-effective ways of ending preventable maternal and child deaths.

This is imperative because 26 percent of all children around the world – nearly 20 million – still do not receive a full course of even the most basic vaccines in countries supported by the GAVI Alliance. In fact, when you count the number of children receiving all 11 vaccines that the WHO recommends, less than 5 percent are fully immunized. As a result, 1.5 million children still die from vaccine-preventable diseases each year.

This can be stopped. We have a unique opportunity in front of us now: to immunize another 300 million children between 2016 and 2020, and produce a tenfold increase in the proportion of children who are fully immunized with WHO-recommended vaccines. The result: 5 to 6 million more deaths averted by 2020.

This unprecedented scale-up would require GAVI to mobilize $7.5 billion in additional investments over the next five years ($1.5 billion per year), which would generate $80 billion to $100 billion in economic benefits, including healthcare savings in developing countries.

Attainment of this will require bold investments by all partners, including the United States. Historically, we’ve seen significant bipartisan support for immunization, with the Obama Administration requesting a record $200 million in its fiscal 2015 budget for GAVI. Overall, the United States has invested about $1.2 billion in GAVI since 2001.

But the solution comes not just from donors. Poor countries also are making significant financial contributions. As their economies grow, they will nearly triple co-payments for GAVI-supported vaccines in the next five years to $1.2 billion, and they will invest billions more directly in their own immunization programs.

Vaccines are a proven, sustainable approach to development, providing lasting benefits for maternal and child health. Just like children need boosters to ensure lasting immunity, American leadership emerging from Acting on the Call is our booster shot to ensure that all mothers and children have a fair start at a healthy life and contribute to their countries’ healthy future.

Berkley is CEO of the GAVI Alliance.