I have spent much of my career responding to infectious diseases in places where vaccines were desperately needed but not always available.

In Haiti, I watched a patient die of tetanus, their body seized by violent, agonizing spasms until they could no longer breathe. Watching someone die that way from a disease a simple vaccine can prevent is something I have never forgotten.

In 2014, I worked in an Ebola treatment unit established within a local hospital in Sierra Leone. I watched mothers travel for hours through communities devastated by the epidemic to bring their children to the hospital for whatever vaccines were available. They understood something Americans increasingly seem to be forgetting: The ability to prevent a deadly infectious disease is an extraordinary privilege.

I have also seen what happens when science gives us that ability.

The development of an effective vaccine against Zaire ebolavirus (EBOV) transformed our ability to respond to Ebola. During the 2018-2020 outbreak in the Democratic Republic of the Congo, more than 300,000 people were vaccinated, helping protect those at risk and slow transmission. Since then, the vaccine has been deployed successfully in multiple outbreaks, helping break chains of transmission and prevent countless infections and deaths.

Today, we are being reminded of the value of that achievement by its absence.

The Democratic Republic of the Congo is now confronting the largest Ebola outbreak in its history, caused by Bundibugyo virus (BDBV). Unlike EBOV, there is no licensed vaccine against it. Scientists are racing to change that, with the first Phase 1 trial of a BDBV-specific vaccine beginning in July. During an outbreak, every day matters. Every infection prevented can mean another person who does not become sick and another family that does not lose someone they love.

That is what makes what is happening simultaneously in the United States so difficult to comprehend.

On Monday, President Trump signed an executive order establishing what his administration calls the “Gold Standard Childhood Vaccine Recommendations.” The order divides childhood vaccines into different categories, pushes states to reconsider school vaccination requirements, and calls for childhood vaccines to be administered at separate appointments “to the maximum extent feasible.” It specifically calls for eventually replacing the combined measles, mumps, and rubella vaccine with three separate vaccines.

There is no evidence-based public health rationale for making routine vaccination more cumbersome.

Combination vaccines allow children to receive protection efficiently and on schedule. Requiring additional visits creates more opportunities for missed appointments and delayed vaccination, especially for families who cannot repeatedly take time off work or arrange transportation and childcare.

Delaying vaccination does not make children safer. It leaves them vulnerable for longer.

More troubling is the rationale surrounding these changes. On Monday, Trump again invoked autism while announcing the policy. Yet decades of research involving millions of children have found no causal relationship between vaccines and autism.

We should not reopen scientific questions because political leaders dislike the answers. And we certainly should not redesign childhood vaccine policy around claims that have repeatedly been disproven.

The consequences are no longer theoretical. We are already seeing what happens when vaccination rates fall.

Measles was declared eliminated from the U.S. in 2000. As of Tuesday, 2,465 measles cases have already been reported — the highest annual number in 35 years. Vaccination coverage among American kindergartners has fallen from the levels needed to reliably prevent outbreaks.

The problem is not that these vaccines have stopped working. Two doses of MMR remain about 97% effective against measles.

What has changed is the number of susceptible people these pathogens can find.

Similar warning signs are appearing elsewhere. Diphtheria and other vaccine-preventable diseases continue to exploit gaps in routine immunization around the world. These diseases do not care whether those gaps were created by lack of access, conflict, misinformation, or political decisions. They simply take advantage of them.

Once these diseases return, the costs are enormous. A recent analysis estimated that a 2025 measles outbreak in New Mexico cost an estimated $5.4 million — about $53,000 for each of its 100 confirmed cases. In comparison, the federal government can purchase a dose of MMR vaccine for about $27 through the Vaccines for Children program. The contrast is striking — prevention costs dollars; responding to a preventable outbreak can cost millions.

This is one of the paradoxes of public health: Success is often invisible.

When vaccination works, there is no outbreak. A child does not develop measles. A pregnant woman does not contract rubella. A patient with a contaminated wound does not die of tetanus. A person who comes into contact with someone who has Ebola does not develop Ebola.

Nothing happens. In that silence lies the paradox of prevention: When vaccines work, we forget the diseases they protect us from.

I worry that is where the United States is heading.

The greatest danger of this executive order may therefore extend beyond any individual change to the vaccine schedule. It is the message the federal government is sending about vaccines and science itself.

For decades, parents have been told — correctly — that childhood vaccine recommendations are based on evidence reviewed by scientists, clinicians, epidemiologists, and independent experts. Now the federal government is suggesting that perhaps combination vaccines were a mistake, perhaps the schedule is unsafe, perhaps vaccines should be separated, and perhaps long-standing school vaccination requirements have gone too far.

For parents already uncertain about vaccination, those signals matter. I have written previously about how anti-vaccine rhetoric has transformed conversations between doctors and patients. I see it in my own practice: Patients with puncture wounds or animal bites sometimes decline tetanus vaccination, even when recommended to prevent a potentially fatal disease. What was once a routine conversation has become a negotiation over whether vaccines themselves can be trusted. This executive order risks making those conversations even harder at the moment when trust matters most.

Public health depends on trust. I have seen this firsthand during outbreaks. When communities trust health authorities, people come forward for testing, bring their children for vaccination and seek treatment early. When trust collapses, rumors spread faster than pathogens, vaccination campaigns falter and outbreaks grow.

The consequences will extend beyond the U.S. American scientific institutions have helped shape global vaccine policy for generations, and U.S. funding and technical guidance support immunization programs around the world. Changes in American vaccine policy therefore do not occur in isolation. They can influence how vaccines are perceived, recommended, and delivered far beyond our borders — particularly in countries that rely on international support for vaccination programs.

We have already seen how U.S. vaccine policy debates can reverberate globally. Efforts to alter vaccine formulations or question long-established vaccine practices can create uncertainty for international immunization programs that depend on affordable, readily available vaccines, and carefully coordinated supply chains. At a time when global vaccination coverage remains fragile, exporting doubt about vaccines may be as consequential as exporting policy itself.

A parent thousands of miles away may never read an American executive order. However, they may hear that the U.S. changed its vaccine recommendations because of safety concerns, or that America wants to separate vaccines that have been safely administered together for decades.

Misinformation crosses borders as easily as viruses do.

That is why the contrast with what is happening in Central Africa is so striking.

In the Democratic Republic of the Congo, scientists and public health workers are racing to develop a vaccine against Bundibugyo virus, because people are becoming infected and dying from a disease for which we do not yet have a licensed vaccine.

In the United States, we already possess extraordinarily effective vaccines against diseases such as measles, tetanus, polio, and diphtheria — and our government is choosing to make their delivery more complicated while casting doubt on the science supporting them.

These may seem like unrelated stories. They are not.

Together, they illustrate one of the central lessons of modern public health: Vaccines are most appreciated when we do not have them.

In the short term, this executive order will create confusion about childhood vaccination. In the medium term, it risks reducing vaccination coverage and creating larger pockets of susceptible children. That means more outbreaks, hospitalizations, resources spent controlling diseases we already know how to prevent, and potentially more deaths.

The longer-term damage may be even greater. If Americans lose trust not only in vaccines but in the institutions responsible for evaluating scientific evidence, rebuilding that trust could take generations. And if the United States retreats from evidence-based vaccine policy, the consequences will reverberate far beyond our borders.

We should be strengthening public health: developing vaccines for emerging and reemerging threats, improving surveillance, making vaccination easier to access, and helping parents understand the evidence.

Instead, we are making proven vaccines harder to receive while scientists elsewhere race to create vaccines they desperately wish they already had.

I have seen what the world looks like without vaccines.

We should not choose to go back there.

Krutika Kuppalli, M.D., is an infectious diseases physician and former World Health Organization medical officer whose work has focused on vaccines, emerging infectious diseases, and outbreak preparedness and response. She served as medical director of an Ebola treatment unit in Sierra Leone during the 2014–2016 West Africa Ebola epidemic and has supported outbreak and vaccine efforts in Africa and globally.