Moderna Inc. shares are selling off Wednesday, after the Trump administration took aim at the science behind the biotechnology company’s vaccines and said it would cancel some contracts and stop funding mRNA drug development.

President Donald Trump hailed as a “medical miracle” the mRNA vaccines developed to combat the deadly COVID-19 pandemic in 2020. Now, his health secretary Robert F. Kennedy Jr., is effectively halting the vaccine technology’s advancement.

This was one in a continuing line of moves that has put RFK Jr.'s vaccine skepticism into public policy, though scientists say the vaccines are safe.