That seems a bit revisionist. To my knowledge, Donald Trump was always a vocal supporter of the Covid vaccine. Kamala Harris and Joe Biden were the ones sowing doubt about it - right up until they won the election. Harris, in particular, described Trump as irresponsible for advocating for Project Warpspeed and suggesting that people should take a Covid vaccine before it had gone through the full approval process.

I think you may be getting their personal stances confused with the partisan arguments about vaccine mandates that have evolved in the year since.