Declaration linked below.
Starting August 31, all vaccinated tourists from the US, Canada, and Japan will need a negative test (PCR or Antigen) done no more than 72 hours prior to arrival in Italy. This declaration is in effect through Oct. 25.
Here's a Google translation from the below declaration...
"To people who have stayed or transited, in the previous fourteen days, in Canada,
Japan and the United States of America, without prejudice to the provisions of Article 4, paragraph 3, of the ordinance of the Minister of Health of 29 July 2021, for the purpose of entering the territory it is also mandatory to present it to the carrier upon boarding and to anyone who is deputy to carry out the checks, of the certification of having submitted, in the seventy-two hours prior to entry into the national territory, to a molecular or antigen test, carried out for swab medium and negative result."
"This ordinance takes effect from August 31, 2021 and until October 25, 2021."