Trump was the one who approved operation Warp Speed which set the ground stage for all of the vaxx nonsense, Biden just let it continue really.

A lot of initial Covid insanity falls squarely on him, though the only thing I'll let him on is that he seemed to make the mistake of trusting other people to make the right call and let people like governors and scientists operate independently. A very common failure of his first term.

This doesn't absolve him of responsibility for things that happened, but only it was done out of stupid naivety (another common problem with his first term) rather than malice.