Vanna and the Big Put: unusual suspects in a market mystery

Risk.net is citing research from MPI, J.P. Morgan and Societe Generale in their analysis of January 24th, 2022 market reversal: “MPI, which runs a replication index tracking 20 large systematic traders, says those firms (most likely) cut their S&P 500 exposure from 6.5% on January 18 to 0% by January 24.”