It's a fairly logical position by Tsitsipas who never publicly backed nor opposed vaccination. He was hesitant about doing it, only opting to do it after the Australian Open imposed a vaccine mandate. The Serbian is yet to commit to doing the same which is why Tsitsipas said about Djokovic when asked:
“It is his choice – I respect it. Everyone has the freedom to decide. I will go to Australia. I don’t promote vaccination, but I’m not even against it. I support anyone who wants to do it. I
am not a doctor, I am an athlete and my outlook may not be the best
when it comes to medicine. I will be vaccinated this year. I do it to
have a normal life.”
Per reports coming from his native Serbia Djokovic is increasingly likely to play at the event which again won't surprise anybody. Whether he will publicly address the matter and confirm vaccination remains to be seen but it's unlikely given his previous positions on such matters. As for Tsitsipas, on his the new season he said this:
“For me it’s like starting from scratch, I find myself facing a completely new challenge. I felt pain in the last two years but I played anyway, until I decided to have surgery in Belgium. I’m
very happy. I’m using a muscle that I almost didn’t know I had because I
wasn’t using it to protect the joint, I changed my style of play.”