The first 100 days of President Donald Trump’s second term have been filled with mass firings, cancellations of research grants, university funding cuts and questions over what should be studied.

Thousands of people have been let go at federal agencies and critical research has been put on hold. Additionally, Health and Human Services Secretary Robert F. Kennedy Jr. has questioned the safety and efficacy of vaccines and antidepressant medications despite dozens of studies proving they are safe and effective.

Doctors and public health specialists critical of the administration tell ABC News they view these actions as an “attack” on science, damaging the reputation of respected agencies and by questioning what is believed to be established science.

“It’s completely unprecedented,” Steve Cohen, senior vice dean of Columbia University’s School of Professional Studies and a professor of public affairs at Columbia’s School of International and Public Affairs, told ABC News. “It’s frankly a little unhinged. I’ve never seen anything like it.”

The White House did not respond to ABC News’ request for comment.

An HHS official told ABC News that framing the actions of the admiration as an “attack” is “fundamentally dishonest.”

“Further reviewing pharmaceutical products with gold standard science and common sense is not an'”attack on science’ — it’s what the American people have asked for and deserve,” the official said. ” Let’s be clear: Secretary Kennedy is not anti-vaccine — he is pro-safety, pro-transparency, and pro-accountability.”

Thousands of layoffs

Earlier this month, HHS began to lay off 10,000 workers as part of a massive restructuring plan.

Sources previously told ABC News that affected offices included most of the Centers for Disease Control and Prevention’s Office on Smoking and Health, key offices in the Center for Tobacco Products, most of the National Institute for Occupational Safety and Health, and the entire assisted reproductive technology team at the CDC.

There have also been local impacts in communities due to federal layoffs. ABC News previously reported in March, the CDC was poised to send its lead ‘disease detectives’ to Milwaukee amid an ongoing lead crisis in schools, but the entire division was cut under sweeping HHS layoffs, leaving local health officials without help they were relying on.

Erik Svendsen, the director of the division that oversaw the CDC’s Childhood Lead Poisoning Prevention branch, previously told ABC News that what’s happening in Milwaukee is a real world example of the impact of their absence.

“Without us, there is no other unit at the federal level that is here to support them in doing what they need to do,” he said.

On Monday, officials in Milwaukee announced two additional schools are closing due to this crisis

Despite Kennedy saying some programs and employees would soon be reinstated because they were mistakenly cut, it still leaves thousands of federal employees without jobs.

Scientists have also been laid off at NASA, the Environmental Protection Agency, the Department of Agriculture and the National Oceanic and Atmospheric Administration.

Cohen said these firings have put studies on hold and have greatly reduced the capacity of the federal government to review research.

“Scientists inside agencies, whether they’re environmental scientists or medical scientists or people focusing on vaccines or drugs, are being fired, and so some of the research capacity in Washington, in the federal government is being eliminated, and also their ability to judge proposals from universities,” he said.

“The only place I haven’t seen [firings] happen yet are the laboratories,” Cohen added.

Cuts that are currently proposed or have already been implemented include the elimination of the Office of Infectious Disease and HIV Policy, created by Brett Giroir, the former U.S. assistant secretary for health.

Giroir, who helped convince Trump in his first term to set a goal to end the HIV epidemic in the U.S., wrote in a post on social media last week that the president could ruin his legacy and mission with such cuts.

Canceling research grants, funding cuts to universities

Millions of dollars’ worth of grants have been terminated at the National Institutes of Health related to studies involving LGBTQ+ issues, gender identity and diversity, equity and inclusion (DEI) because they do not “effectuate” the “priorities” of President Donald Trump’s administration, according to copies of termination letters sent to grant recipients and viewed by ABC News.

Dr. Harold Varmus, a cancer researcher at Weill Cornell Medicine in New York City and former director of the NIH, said these terminations are “detrimental” because they may be affecting people in the middle of clinical trials, or affecting the early stages of experimental work.

Research projects focusing on minority populations have major benefits, Varmus noted.

“The purpose of health research in this country is to address problems faced by everybody and to explore every facet of a population that may affect their health,” he said. “To single out certain categories of individuals who would not be appropriate to study seems ludicrous to me … one of the great strengths of America is that we are diverse.”

Universities have also been threatened with funding cuts — or have seen funds frozen — if they don’t fulfill their obligations under Title VI of the Civil Rights Act to protect Jewish students on campus and to end race-based programs.

Cohen believes universities are at odds with the administration because some on the political right view universities as “left wing.” By “weakening the finances of universities, they can force them to change the ideologies that they believe are being promoted in the classrooms,” he argued.

The problem with this idea, according to Cohen, is that the administration’s actions are hurting the least ideological parts of universities, such as engineering schools or medical centers. At Columbia, for example, several institutes and centers are conducting Alzheimer’s research, he said.

“Those are the places that are being attacked,” Cohen said. “It’s pretty ironic, but the greatest danger, actually, is that one of America’s fundamental economic strengths is the creativity and the innovation of our scientists, and that is now under attack by the Trump administration.”

Questioning safety, efficacy of vaccines

Kennedy has shared vaccine skepticism in the past and has continued to do so as HHS secretary.

In the wake of several ongoing measles outbreaks and over 800 cases so far this year, Kennedy has shared contradicting views about vaccines.

In a post on X on April 6, he said that “most effective way to prevent the spread of measles” is to receive the measles, mumps, rubella (MMR) vaccine. However, in a post later that evening, he said more than 300 children have been treated with an antibiotic and a steroid, neither of which are cures for measles.

Dr. Peter Hotez, a professor of pediatrics and molecular virology at Baylor College of Medicine in Houston, said the statements Kennedy has made in support of the MMR vaccine are “half-hearted.”

“The reason I say ‘half-hearted’ or insufficient is because each time he talks about using the MMR vaccine, he qualifies it,” Hotez told ABC News. “He then draws this false equivalency between either getting the MMR vaccine or this cocktail of interventions that would do absolutely nothing.”

Last month, HHS confirmed that the CDC will study “all the potential culprits” including whether vaccines cause autism despite numerous existing studies already showing there is no link.

Hotez said epidemiologic studies show that children who received either the MMR vaccine, or vaccines containing thimerosal — a compound used as a preservative in vaccines — are not more likely to be diagnosed autism than kids who didn’t receive those vaccines.

Additionally, Hotez said about 100 genes have been identified that are involved in the development of autism, many by the Broad Institute at Harvard and the Massachusetts Institute of Technology.

He believes rising rates of autism diagnoses are likely due to wider testing and expanding diagnostic criteria. Hotez added that there could be an environmental exposure influencing autism genes, but that it’s not vaccines.

In 2017, he discussed with Kennedy an investigation looking at “about half a dozen chemical exposures” in early pregnancies but Kennedy “had no interest,” according to Hotez, who later documented these conversations in a book he published in 2018.

“He apparently seems to not understand the science or doesn’t care about the science. He’s got his fixed beliefs and doesn’t want to let any of the facts or scientific findings get in the way of his fixed belief,” Hotez said. “And it’s completely irresponsible having someone like that as Health and Human Services secretary.”

Claims around antidepressant use

Earlier this year, Trump issued an executive order to study the use of several medications including antidepressants and antipsychotics.

The order called for the formation of the “Make America Healthy Again” commission — to be chaired by Kennedy — with an aim to understand chronic diseases.

Among the goals of the commission is to “assess the prevalence of and threat posed by the prescription of selective serotonin reuptake inhibitors, antipsychotics, mood stabilizers, stimulants, and weight-loss drugs.”

Dr. Joseph Saseen, associate dean for clinical affairs and a professor in the departments of clinical pharmacy and family medicine at the Skaggs School of Pharmacy and Pharmaceutical Sciences at the University of Colorado, said there are plenty of studies and analyses in the medical literature looking at the prevalence of SSRIs.

“We have an overwhelming amount of information,” he told ABC News. “These medicines, particularly SSRIs, are the most frequently prescribed antidepressants for patients with major depressive disorder. There is a plethora of information evaluating efficacy in a broad range of patient populations for which these medicines are indicated.”

Saseen says these medications do have side effects, just like any drug, but the benefits significantly outweigh the risks for most people in the general population who have major depressive disorder and anxiety disorders.

Kennedy has also falsely linked the use of antidepressants to school shootings and claimed during his Senate confirmation hearings that members of his family had a harder time stopping SSRI use than heroin use.

Experts have said there is no evidence that equates ending the use of antidepressants to ending the use of heroin or to suggest that people on SSRIs are more likely to be violent.

Saseen said it’s reasonable to question scientific research, either to reaffirm or dispute findings, but it must be done following the scientific method.

“Question it the real way, not the cowardly way,” he said. “The cowardly way is labeling things as threats or as bad without taking a scientific approach. The key is you need to use appropriate methodologies, not vocal inflections and very triggering and polarizing words to create an uprising.”

ABC News’ Dr. Jade Cobern, Cheyenne Haslett, Will McDuffie and Sony Salzman contributed to this report.