We had a spate in a few months from December through to April: the U.K., Brazil, S.A. and India all producing ones of concern, with others emerging alongside them... However, and m probably tempting fate writing this, there hasn't been anything significant for a while....
I'm wondering if that's because Delta is, firstly, so transmissible that there's little scope left for any significant change that would give a new variant an edge and, secondly, Delta is able to continue to propagate despite vaccines, albeit that the vaccines take the edge off and reduce its harmful effects...