Reb Yosef is correct: Kissing the Rebbe’s hand is a lot more efficient way of spreading any infectious disease rather than simply shaking hands.
In reality, there will obviously be real changes in salutation and recognition behaviors, at lease for the near-term. There are many ways to show kovod for your rebbe, w/o direct physical contact. That is just as much for the Rebbe’s well-being as your own.