We have each had the honor and privilege of serving as director of the Centers for Disease Control and Prevention, either in a permanent or an acting capacity, dating back to 1977. Collectively, we spent more than 100 years working at the C.D.C., the world’s pre-eminent public health agency. We served under multiple Republican and Democratic administrations — every president from Jimmy Carter to Donald Trump — alongside thousands of dedicated staff members who shared our commitment to saving lives and improving health.

What the health and human services secretary, Robert F. Kennedy Jr., has done to the C.D.C. and to our nation’s public health system over the past several months — culminating in his decision to fire Dr. Susan Monarez as C.D.C. director days ago — is unlike anything we had ever seen at the agency and unlike anything our country had ever experienced.

Mr. Kennedy has fired thousands of federal health workers and severely weakened programs designed to protect Americans from cancer, heart attacks, strokes, lead poisoning, injury, violence and more. Amid the largest measles outbreak in the United States in a generation, he’s focused on unproven treatments while downplaying vaccines. He canceled investments in promising medical research that will leave us ill prepared for future health emergencies. He replaced experts on federal health advisory committees with unqualified individuals who share his dangerous and unscientific views. He announced the end of U.S. support for global vaccination programs that protect millions of children and keep Americans safe, citing flawed research and making inaccurate statements. And he championed federal legislation that will cause millions of people with health insurance through Medicaid to lose their coverage. Firing Dr. Monarez — which led to the resignations of top C.D.C. officials — adds considerable fuel to this raging fire.

We are worried about the wide-ranging impact that all these decisions will have on America's health security. Residents of rural communities and people with disabilities will have even more limited access to health care. Families with low incomes who rely most heavily on community health clinics and support from state and local health departments will have fewer resources available to them. Children risk losing access to lifesaving vaccines because of the cost.......

We have a message for the rest of the nation as well. This is a time to rally to protect the health of every American. Congress must exercise its oversight authority over Health and Human Services. State and local governments must fill funding gaps where they can. Philanthropy and the private sector must step up their community investments. Medical groups must continue to stand up for science and truth. Physicians must continue to support their patients with sound guidance and empathy.

And each of us must do what public health does best: look out for one another.