Professor Luke O Neill says he was left shaken after he was attacked on the street in Dublin by an anti-vaxxer.
The Trinity College immunologist says he is used to online abuse, and blocks those who target him on social media.
However, Professor O'Neill told The Pat Kenny Show there was one incident when he was challenged on the street.
He recalled: "Around three months ago I was walking down Grafton Street one lunchtime, and some guy pulled me by the collar... he pulled me back. I got a fright.
"He started shouting at me 'oh you're pro-vaccine, you're damaging children'... there is the anti-vax lobby out there.
"He was struggling himself with various issues, is the way I would put it. So I just kept walking, but it did give me a fright I must say."
Professor O'Neill said 'anti-vaxxers mobilise' and come at many different people on social media.
He said: "I block it all - I never see it because you can block it on Twitter. In my email, it all goes to spam.
"But it is going on. You have to expect it - there isn't much you can do about it."
Separately, Professor O'Neill said he's not concerned about the return of students to school, ahead of a phased reopening getting underway from Monday.
He explained: "The risk of keeping kids out of school... the harm that does... far outweighs any risk the virus might spread from schools. I think it's going to be fine.
"There is a risk, of course there is. But that risk is far outweighed by the harm that's done by keeping kids out of schools."
