(Sorry if already posted...)
Effective December 16th through January 31st, vaccinated folks from (among other countries) US and Canada still need to be tested, but for rapid-antigen tests the time limit is now 24 hours prior to arrival in Italy (it had been 72 hours.) For PCR tests, it's still 72 hours. Changes also seen to those coming from the EU. Text below (in Italian, auto-translate works).