Washington DC - President Donald Trump took to social media to demand drug companies "justify the success" of treatments to combat Covid-19, casting doubt on the success of his own vaccine program.

Complaining that the CDC was being "ripped apart" by debates over the effectiveness and safety of Covid vaccines, Trump explicitly called out Pfizer in a rambling post on Truth Social.

"Many people think they are a miracle that saved Millions of lives. Others disagree!" he said of the shots.

"With CDC being ripped apart over this question, I want the answer, and I want it NOW. I have been shown information from Pfizer, and others, that is extraordinary, but they never seem to show those results to the public."

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Trump's demands, as well as recent comments he made seemingly agreeing with Health Secretary Robert F. Kennedy Jr.'s vaccine skepticism, were a notable shift from his usual self-congratulatory tone when it comes to the "Operation Warp Speed" vaccine development program launched at the end of his first term.

"I hope OPERATION WARP SPEED was as 'BRILLIANT' as many say it was. If not, we all want to know about it, and why?" the 79-year-old asked.

There was also a clear reference to the open conflict between RFK Jr. and the CDC, one that reached new levels after the agency's director, Susan Monarez, was abruptly fired.

Kennedy's FDA recently also issued updated approvals for Covid-19 vaccines that massively restrict their availability.

The vaccines have been repeatedly shown to be effective and safe, with severe side effects remaining rare.