@MadScientist It's hard to really establish how frequent it really is. It is such a low frequency that even a single case more or less has significant impact on the X in the "1 in X cases" rate. At most it's a dozen per million. And it's possible that this is linked to the Adenovirus that's being used as a carrier for the viral load, and not the virus itself.
theguardian.com/world/2021/apr/13/… states there's a test