A vial labelled "Pfizer COVID-19 Vaccine" is seen in this illustration taken January 16, 2022. REUTERS/Dado Ruvic/Illustration

(Reuters) -Pfizer and Moderna on Wednesday defended their COVID-19 vaccines as having saved millions of lives worldwide, in separate responses to U.S. President Donald Trump's demand that pharmaceutical companies should justify the success of their pandemic drugs.

In a post on Truth Social, Trump asserted that he has seen "extraordinary" data from companies such as Pfizer, but criticized them for withholding results from the public and the Centers for Disease Control and Prevention.

Pfizer welcomed Trump's demand for openness and pointed to a dedicated section on its website where clinical trial findings and safety updates are posted. Moderna said it would compile previously disclosed research and findings on its website.

"We are immensely proud of the role we played in the historic achievements of Operation Warp Speed," Moderna said, praising the U.S. government's 2020 initiative to accelerate vaccine development, manufacturing and distribution.

Pfizer CEO Albert Bourla called Operation Warp Speed a "profound public health achievement" under Trump's leadership, adding that the program helped in averting over $1 trillion in healthcare costs.

The companies' announcements come amid escalating turmoil at the CDC. Last week, director Susan Monarez was fired less than a month into her tenure after resisting changes to vaccine policy that were advanced by Health Secretary Robert F. Kennedy Jr, who was handpicked by Trump earlier this year.

Her removal sparked the resignation of four senior CDC officials, who blamed the erosion of public health credibility.

Kennedy has also rescinded federal COVID vaccine recommendations for pregnant women and healthy children and halted about $500 million in funding across 22 mRNA vaccine research projects, including those targeting COVID.

As tensions over federal immunization policies and public health directives grow, Florida on Wednesday announced plans to end all state vaccine mandates, including for children to attend schools.

Kennedy is set to testify before the Senate Finance Committee later this week, where lawmakers are expected to probe the CDC's leadership crisis and ongoing policy shifts.

Pfizer also said new information on its latest vaccine strain, recently cleared by the U.S. Food and Drug Administration, will be published in the coming days.

(Reporting by Mrinalika Roy and Mariam Sunny in Bengaluru; Editing by Shinjini Ganguli and Mohammed Safi Shamsi)