Its not clear there is one catalyst for the pop in the dollar

The market seems immunised against bad coronavirus news, and yet the new on the virus is not improving.

This via STAT (medical news):

  • scientists ... are also keeping an eye on a different mutation with potentially greater implications for how well Covid-19 vaccines work
  • The mutation, identified in a variant first seen in South Africa and separately seen in another variant in Brazil, changes a part of the virus that your immune system’s antibodies get trained to recognize after you’ve been infected or vaccinated. Lab studies show that the change could make people’s antibodies less effective at neutralizing the virus.

(bolding mine - more at the link)

Its not screamingly obvious this is the catalyst, there are also reiisng US yeilds to consider.