(TNND) — President Donald Trump called on drug companies to "justify" the success they claim over COVID-19 vaccines.

“Many people think they are a miracle that saved Millions of lives. Others disagree! With CDC being ripped apart over this question, I want the answer, and I want it NOW,” Trump said in a Truth Social post Monday.

Trump said he’s seen “extraordinary” information from drugmakers that hasn’t been shared publicly.

Trump specifically mentioned Health Secretary Robert F. Kennedy Jr. among those who “rip themselves apart” to figure out if the COVID-19 vaccines work as advertised.

Jennifer Nuzzo, the director of Brown University's Pandemic Center, said Tuesday that there’s no doubt in her mind that COVID-19 vaccines are safe and effective.

“I can't imagine any publicly traded company that was sitting on remarkable data would withhold that from the public,” she said. “But I don't know. I can't comment on things I haven't seen.”

Nuzzo said she’s always in favor of more data from drugmakers, but not because she needs convincing over the vaccine efficacy.

“There are some questions about how best to use COVID boosters going forward,” Nuzzo said. “And I think more reasonable people have raised the idea of what truly are the benefits of the COVID boosters. How best do we use them? What's the best timing? We know the added protection that they provide is short-lived. What's the best way to offer that protection, etcetera. So, there are a number of, I think, reasonable scientific questions that need to be answered. That is not the same as saying the vaccines don't work or that they didn't save millions of lives during the most extreme parts of the pandemic.”

Nuzzo gave Trump credit for “Operation Warp Speed,” which resulted in COVID-19 shots in less than a year.

“President Trump should be supportive of the COVID vaccines, because it was really the kind of signature accomplishment of the first Trump administration,” Nuzzo said.

The U.S. has seen 1.2 million deaths from COVID-19 since the pandemic began in 2020.

About a quarter of those deaths occurred by the time the first Americans were getting COVID-19 shots in December 2020.

By the middle of 2021, about half of the cumulative COVID-19 deaths had taken place.

By that point, the vaccine was available for anyone who wanted it, Nuzzo said.

The last spike in deaths took place in early 2022, and by the beginning of March 2022, the nation had already experienced 80% of the COVID-19 deaths to date.

Nuzzo acknowledged that more Americans died from COVID-19 after vaccines were introduced than before.

“But that doesn't mean that the vaccines didn't protect people. It means that a lot of people didn't avail themselves of the protection of the vaccine,” she said.

She also noted that people avoided the public more in the pre-vaccine era, which limited the spread.

And she said there were “starkly” different death rates among those who were vaccinated and those who were not.

The Centers for Disease Control and Prevention, for example, said in 2023 that people who had gotten an updated COVID-19 shot were 14 times less likely to die than those without a vaccine and three times less likely to die than those who had gotten just the original COVID-19 vaccine.

Meanwhile, Nuzzo lamented what she sees as attempts by Kennedy to leverage concerns over COVID-19 shots to sow doubt about all vaccines.

“In some instances, there are some valid questions that we need to answer about COVID vaccines, but I think what we're seeing is an attempt to kind of capitalize on some uncertainty around COVID vaccines and some disagreement about how best to use COVID vaccines as part of a larger attempt to gut or reorder public health systems,” she said.

The Food and Drug Administration last week limited its approval for new COVID-19 vaccines from Pfizer, Moderna and Novavax.

All of the vaccines are approved for people 65 and older, and approval for younger people was narrowed to those with underlying health conditions.

RELATED STORY: Who should parents trust? American Academy of Pediatrics, CDC offer different shot advice

Only a Moderna vaccine is approved now for kids as young as 6 months. The Pfizer vaccine is approved for kids down to age 5.

FDA Commissioner Marty Makary said via social media last week that all adults who want a COVID-19 shot can still get one.

But Nuzzo said the federal health agencies are creating barriers for people who want to get the shots.

“There is a change occurring in the marketplace that is now going to make it harder for even people who qualify, even people who are at high risk for severe illness, to get the vaccine,” she said.

If people can’t just stroll into a pharmacy and get a COVID-19 shot, if they need doctor approval, or if the shots cost more out of pocket for people, then fewer will get them, Nuzzo said.

“That, to me, is not consistent with an overall belief that people should be able to do their own research and make these decisions on their own, to give them more freedom over their own health,” Nuzzo said. “To me, this is taking away people's freedoms by making it harder for them. It's then shifting strains to the health care system. You shouldn't have to get into an appointment to see your medical provider in order to make a decision at this stage of the game about getting a COVID booster. There is no medical or epidemiologic justification for that. By saying that you have to do it in consultation with your medical provider, you are signaling to people that in some way these vaccines may be harmful. And there is no evidence of that.”