The move came after an 18-year-old woman died of a blood clot Thursday after receiving an initial dose of AstraZeneca on May 25, Xinhua reported.
According to local media reports, the young woman suffered from autoimmune thrombocytopenia (meaning that she had a low blood platelet count) and was on double hormone therapy.
An investigation is underway to find out whether she had disclosed this information during the vaccine intake procedure, Italian news agency Ansa reported.
"The epidemiological scenario has changed, and so has the relationship between the benefits of vaccination and the potential risk of unusual blood clots," Franco Locatelli, coordinator of the Technical Scientific Committee (CTS) which gives advice to the government on how to handle the pandemic, said at the press conference.
The CTS recommends that people under 60 who received an initial dose of AstraZeneca be given a different vaccine for their second dose, Locatelli said, adding that this move represents "an excess of caution".
Over 40.7 million doses of vaccine have been administered in Italy and over 13.7 million people, or 25 percent of the population aged over 12, have been fully inoculated, according to the latest tally from the Ministry of Health on Friday.