[thedevindevops]

It's not interactive but the wikipedia article on herd immunity demonstrates it perfectly though I would try to steer your friend in a different direction as herd immunity can be used as an excuse not to get vaccinated (see Free Rider Problem), instead try to get to the root of their uncertainty and try to get them into a mindset where they consider others rather than just their own welfare.

[AlexDanger]

This person is very considerate. They are already in a mindset where they will help others. They just dont see how herd immunity works.

I'm looking for interactive simulations that show how a certain vaccination rate 'tips the scales' and keeps the whole community safe. Something like this but a little more user friendly (eg using sliders and slick animations):

https://www.software3d.com/Home/Vax/Immunity.php