The Facebook page of the South East Tuscany health authority was inactive for a spell on Wednesday after being clogged up by around 3,000 comments from anti-vaxxers.
The comments blasted vaccines and called health workers involved in giving jabs "Nazis".
Postal police in Arezzo have opened a probe after a health authority official filed a complaint.
The initials 'VV' appear in the comments, which could be evidence of a link to a anti-vax group, investigators suspect.
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