It’s a movement organized in only the loosest of terms. It’s anti-vaccine and anti-science. It’s pro-medical freedom and pro-alternative medicine. But growth in the movement’s ranks has many in and out of government fearful that this campaign cycle will accelerate its spread, consolidate its strength and cement its place in the political milieu.

“It’s going to get worse before it gets better,” said Dr. Jerome Adams, U.S. surgeon general during the Trump administration. “Many of us in public health are deeply concerned that distrust in government and health entities, and a political campaign in which candidates are openly and vigorously arguing that people should ignore the advice of health experts, could have detrimental impacts for years to come — no matter who wins.”

Former President Donald Trump’s administration marshaled unprecedented federal resources to develop and promote a Covid vaccine in record time. But within a few weeks of its arrival, lingering resentment over lockdowns and mistrust of government led to a widespread backlash, particularly among conservatives, that persists almost three years later. Nearly four in 10 Republicans say they will “definitely” or “probably” get the new vaccine, according to polling conducted by Morning Consult and POLITICO, while nearly eight in 10 Democrats expect to seek out the updated shot.

That skepticism is bleeding over into other vaccines, like those that prevent measles, mumps and rubella. Dr. Umair Shah, Washington state’s secretary of health, said it may even take the death of an influential figure to a vaccine-preventable disease to shock the public back to wider acceptance of immunizations.

“I’m really concerned, and a lot of people in public health and health care are very concerned, that this is the beginning of a really rough and tough time,” Shah said. “Unfortunately, people are going to get sick. We’re going to lose lives.”

For decades, being openly skeptical of vaccines made one a pariah in all but the smallest of political circles. Both parties generally accepted that modern science had made essential breakthroughs in health care. To cast doubt on them placed you on the fringe. But public health officials fear those days are increasingly numbered.

Robert F. Kennedy Jr., who notched 15 percent support in a Harvard-Harris poll of the Democratic presidential primary field earlier this month, is running on his anti-vaccine bona fides. Florida Gov. Ron DeSantis, a Republican, is campaigning on his work to promote “medical freedom” and has said he would put Kennedy on a task force to investigate government overreach in medicine if elected president. Vivek Ramaswamy, a biotech entrepreneur also running for the Republican nomination, has touted his plans to “expose and ultimately gut” the FDA and floated Kennedy as a running mate.

While these candidates are trailing in the polls, their followings are certain to outlast the campaign. Lingering resentment over pandemic restrictions is fueling further skepticism around public health, potentially leading to even lower vaccination rates, wider spread of disease and an inability to address future pandemics.

“Hundreds of thousands of Americans have died in this pandemic because of the bad information about vaccines and treatments,” said Dr. Ashish Jha, dean of the Brown School of Public Health and former White House Covid-19 response coordinator under the Biden administration. “I certainly am worried about what happens over the next three to five years.”

The data show the vast majority of Americans still trust science, listen to doctors and vaccinate their children. But the growing number of those who don’t threatens to undo generations of work combatting deadly and debilitating diseases that haven’t widely circulated for decades.