Fifty years ago this week the landscape of health care in America changed forever when President Lyndon Johnson signed the landmark amendment to the Social Security Act, thus beginning the Medicare and Medicaid programs.

Before 1966, roughly half of all seniors were uninsured, living in fear that the high cost of health care could propel not only them, but their families, into poverty. And before the advent of Medicaid, far too many people with disabilities and lower-income working Americans were unable to afford the medical care they needed to remain healthy and productive.

Both Medicare and Medicaid have not only greatly reduced the number of uninsured Americans but have become the standardbearers for quality and innovation in American health care. Today, Medicare and Medicaid cover nearly 1 out of every 3 Americans — more than 100 million people.

About 55 million Americans depend on Medicare to cover 23 types of preventive services, including flu shots and diabetes screenings. Medicare also covers hospital stays, lab tests and critical supplies such as wheelchairs, as well as prescription drugs.

Medicaid provides comprehensive coverage to more than 70 million eligible children, pregnant women, low-income adults and people living with disabilities. It covers essential services such as annual checkups, care for new and expecting mothers and dental care for kids from low-income families.

As we look to the next 50 years and beyond, Medicare and Medicaid have a critical role to play in the next evolution of our nation’s health care system.

We are working hard to modernize the health care system to deliver better care and spend health care dollars more wisely. We are finding better ways to ensure that the right care is accessible and delivered to the right person at the right time, every time. We are deploying tools such as electronic health records to improve the coordination of patient care and lower costs.

The U.S. Department of Health and Human Services has set an ambitious goal and timeline to move the Medicare program toward paying providers based on the quality of care delivered, rather than the quantity of care they give patients.

Medicare and Medicaid are among the most efficient health insurance programs in the world. Every day, dedicated teams work to provide Americans with access to the quality care they need, fostering innovation, combatting fraud and protecting patients, and ultimately taxpayers. They will continue to transform to create a health care system that delivers better care, spends health care dollars more effectively and results in a demonstrably healthier populace.

Since the passage of the Affordable Care Act five years ago, more than 16.4 million uninsured people have gained health coverage. That’s the largest reduction of the uninsured in four decades.

Working together, Medicare, Medicaid and the ACA have brought security to our families, neighbors and friends who previously lived in fear of having to choose between a necessary surgery and affording groceries.

The ACA further strengthened Medicare by offering a new range of preventive services at no cost, and giving discounts on drugs to Americans who are in the coverage gap (aka “the doughnut hole”). Thanks to the ACA, people who have original Medicare could qualify for a yearly wellness visit and receive free preventive services, such as mammograms and diabetes screenings.

And should they reach the so-called Medicare drug “doughnut hole,” they will get a 55 percent discount on covered brand-name drugs and a 35 percent discount on generic drugs.

For example, in Maine, 214,561 individuals with Medicare used one or more free preventive service in 2014. At the same time, Mainers with Medicare have saved nearly $46 million on prescription drugs because of the Affordable Care Act. In 2014 alone, 17,348 individuals in Maine saved more than $15 million or an average of $867 per beneficiary.

This is more than shared savings. It has brought many people a new peace of mind and the certainty of ever-better care to our communities. And that is something we can all celebrate.

Rachel Kaprielian is director of the New England regional office of the U.S. Department of Health and Human Services in Boston.