Zanni returns for Italy
The 33-year-old Zanni last played for Italy in the 2016 tournament but injuries have since prevented the Benetton flank from adding to his 99 caps.
He has been called up by O'Shea along with Gloucester flank Polledri, with Leonardo Sarto and Tommaso Allan also returning after being sidelined for the November Tests.
"The exciting aspect in this group is the number of options we are developing and the choices we now have available," said Irishman O'Shea.
"We must continue to build depth and we are aware of having to improve, but we have made important progress compared to a year ago.
"I am aware that we will be judged on the results but we all know the level of play we will face and the challenges that await us in every game, starting by playing the second and third best teams in the world rankings in the space of six days in the first two rounds."
Italy – who took the wooden spoon for a second straight time last year – open against defending champions England on February 4 in the Stadio Olimpico and then go to Ireland for the second round on February 10.
The 34-man squad will travel to Rome for a training camp, where they will be joined by young Benneton props Marco Riccioni and Cherif Traore, who will train with the squad.
A final 31-man squad will be named after that training camp from January 21 to 24.
O'Shea took over in March 2016 and his side shocked former world champions South Africa in November that year, beating the Springboks 20-18 in Florence.
But the former Ireland international has had mixed results with Italy, winning just four of 17 matches, including November Tests against Argentina and South Africa.
Meanwhile, New Zealand legend Wayne Smith confirmed he will join Italy's coaching setup later this year despite being diagnosed with prostate cancer.
The 60-year-old believes the surgery was a success and is already targeting a new role working with Italy in the build-up to next year's World Cup in Japan.
"I'll also be doing two to three weeks with the Italian national team coaches over the year," said Smith.
"I'll attend a couple of camps to have a mentoring-type role with Conor O'Shea and Mike Catt. I have a real passion for Italy, its people and their rugby, so my wife Trish and I are looking forward to getting back there now and again."
Forwards: Simone Ferrari, Tiziano Pasquali, Nicola Quaglio (Benetton), Andrea Lovotti (Zebre); Luca Bigi (Benetton), Leonardo Ghiraldini (Toulouse), Oliviero Fabiani (Zebre); George Biagi (Zebre), Dean Budd, Marco Fuser, Federico Ruzza, Alessandro Zanni (all Benetton); Renato Giammarioli, Maxime Mbanda (Zebre), Giovanni Licata (Fiamme Oro), Sebastian Negri, Abraham Steyn (all Benetton), Sergio Parisse (Stade Francais), Jake Polledri (Gloucester).
Backs: Edoardo Gori, Tito Tebaldi, Tommaso Allan, Ian McKinley (Benetton), Carlo Canna, Marcello Violi (Zebre); Mattia Bellini, Giulio Bisegni, Tommaso Boni, Tommaso Castello, Matteo Minozzi, Edoardo Padovani (Zebre); Tommaso Benvenuti, Jayden Hayward (Benetton); Leonardo Sarto (Glasgow).
Additional players: Marco Riccioni (Benetton) – prop: Cherif Traore (Benetton) – prop