In a message on social media that baffled many scientists, President Trump questioned the effectiveness of the Covid vaccines and demanded that the makers prove that they work.
“Many people think they are a miracle that saved Millions of lives,” Mr. Trump wrote on Truth Social. “Others disagree!”
“I want the answer, and I want it NOW,” he wrote. The president went on to complain that while one manufacturer, Pfizer, had shown impressive figures to him, “they never seem to show those results to the public. Why not???”
It is unclear what data Mr. Trump was referring to. Hundreds of reports have tracked the efficacy of the vaccines since they first debuted in 2021. The shots have saved millions of lives in the United States and elsewhere, dozens of studies have estimated.
Still, in some ways, Mr. Trump’s demand for data is a welcome change from what administration officials have been saying recently about vaccines, said John Wherry, director of the Institute for Immunology and Immune Health at the University of Pennsylvania.
Health Secretary Robert F. Kennedy Jr. has been “blatantly misrepresenting the data,” Dr. Wherry said. As for other administration officials, “they’ve been sort of ignoring data, or claiming the data is false, or talking about anecdotes.”
How effective are the Covid vaccines?
The first clinical trials found that the shots made by Pfizer-BioNTech had an efficacy of 95 percent against symptomatic infection with the coronavirus, far higher than federal officials had hoped for. Moderna and Novavax reported similarly high efficacy numbers for their Covid vaccines.
Since the shots were rolled out, studies worldwide have confirmed their effectiveness. “Every country has done their own real-world analysis,” said Deepta Bhattacharya, an immunologist at the University of Arizona.
One study in Scotland, for example, showed that the vaccine lowered the risk of hospitalization because of Covid by 91 percent. As the coronavirus evolved, however, the original vaccines became less effective at preventing infection.
But they continued to protect against severe disease and death.
Between late September 2023 and August 2024, the shots averted more than 107,000 hospitalizations and nearly 7,000 deaths in the United States alone. The vaccines introduced in the fall of 2024, the most recent for which data are available, showed an effectiveness of about 45 percent against hospitalization.
That number is “more modest, but it’s also occurring in the background of entire population immunity, both from infection and vaccination,” Dr. Wherry said.
Even a 45 percent efficacy “is not nothing, not only from the standpoint of disease burden,” he added. “These vaccines actually decreased health care costs quite substantially.”
Did the manufacturers make the data public?
Yes, the Food and Drug Administration required the companies to submit their data before granting so-called emergency use authorization for the shots. The companies also published the results of their clinical trials in scientific journals.
The data are “right there for anyone to take a look at,” Dr. Bhattacharya said. “It just isn’t true that the data weren’t made public.”
The makers also presented their findings at meetings of independent advisers to the F.D.A. and the Centers for Disease Control and Prevention. The experts discussed the results at length in public meetings before casting votes to authorize and recommend the shots.
Many independent teams have also analyzed the results at length.
“C.D.C. scientists have been tracking the effectiveness of Covid vaccines since they were first rolled out to the public,” said Dr. Fiona Havers, who led a team that collected data on hospitalizations related to Covid.
She resigned from the agency in June, after Mr. Kennedy fired an independent expert panel who advised the agency on vaccines.
Multiple systems at the agency show that the vaccines have prevented hospitalizations and deaths, she said.
Vaccine makers have also published results of follow-up tests on the shots that they tweaked to match later variants.
Clinical trials of these later vaccines could not have been completed in time for them to be available when needed. But the companies conducted other studies to show that the vaccines boosted immunity against the virus, and released that data.
How many lives have been saved by Covid vaccines?
Scientists believe that the vaccines have prevented millions of deaths. A study in the journal Lancet Infectious Diseases estimated that the shots saved 14.4 million lives worldwide in the first year alone.
In the United States, they are thought to have prevented more than 18.5 million hospitalizations and 3.2 million deaths by the end of 2022.
As people have gained immunity from multiple infections and immunizations, the vaccines have proved essential for the most vulnerable members of the population: adults older than 65, those with compromised immune systems, and pregnant women.
Is the chaos at the C.D.C. about Covid vaccines?
In his post this weekend, Mr. Trump said that the C.D.C. is “being ripped apart over this question” of whether the Covid vaccines are effective.
Without evidence, Mr. Kennedy has called the Covid vaccines “the deadliest” shots ever made and has moved to restrict access to them. But the tumult at the C.D.C. is not just about the Covid vaccines.
Since taking office in February, Mr. Kennedy has laid off thousands of agency employees, slashed its budget and contracts by about half, fired its entire panel of vaccine advisers and ousted its director, who was just three weeks into the job.
C.D.C. employees are also reeling from a terrorist attack on the agency last month, even as Mr. Kennedy continues to accuse them of corruption and bias.
“What’s ripping C.D.C. apart is attacks from within this administration on C.D.C.,” Dr. Havers said.
Apoorva Mandavilli reports on science and global health for The Times, with a focus on infectious diseases and pandemics and the public health agencies that try to manage them.
Carl Zimmer covers news about science for The Times and writes the Origins column.
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