One of Italy's premier immunology experts on coronavirus has been given police protection after she was sent a bullet inside a letter threatening her and her family.
Prof Antonella Viola was apparently targeted because of her public backing for children to be vaccinated.
Public figures have come under increased threat in several European countries this week.
A number of French MPs were threatened as they debated a vaccine pass law.
And on Wednesday night, the home of Dutch political leader Sigrid Kaag was attacked by a conspiracy theorist waving a flaming torch and live-streaming it on Facebook.
Colleagues have blamed Dutch far-right party Forum for Democracy for stirring up hatred over vaccinations and other Covid rules. The suspect could be heard chanting far-right slogans.
Another political leader, Gert-Jan Segers, warned that this kind of intimidation was a natural result of a party that called for tribunals or for political opponents to be jailed.
In Italy, immunologist Prof Viola - head of a paediatric research institute in the northern city of Padua - confirmed on Facebook that she had received a bullet and a letter that threatened her or her family with being shot if she did not say no to children being vaccinated.
"These people are anti-vaxxers who know only how to hate, reject logic and laws and create tension and violence," she said, insisting she would always give science a voice and speak to those who listened.
Italy began vaccinating children aged five to 11 last month, but the jabs are not compulsory.
- So far Austria is the only country in Europe bringing in mandatory Covid vaccinations for children - with a law coming in next month for everyone over 14
- Germany is planning mandatory vaccinations for adults
- Italy will require over-50s to have the jab until June
- Greece starts on over-60s this month and the Czech Republic in March.
"I will continue to advise parents to vaccinate their children because that's right," Prof Viola told Italy's Ansa news agency.
Debate around vaccinations has become increasingly tense as rules are tightened. After three nights in France's National Assembly, MPs backed the first reading of a bill early on Thursday that will require a Covid vaccination pass for much of public life.
President Emmanuel Macron enraged political opponents when he said he wanted to "piss off" unvaccinated people by "limiting as much as possible their access to activities in social life".
Protests have taken place in several cities in Germany this week and police used pepper spray and batons during clashes in Munich.