[venomsnake]

Well ... it is simple math. If the vaccine is effective 95% (pretty good on its own) and you come in contact with 10 sick people you have a good 40% chance to catch it.

That is the whole things with vaccines - the herd immunity is as important in protection as the vaccine itself. It is virtuous positive feedback loop.

[bobbydavid]

This is the part most people don't get, on either side. You're vaccinated? Not a magic bullet, you rely on others around you. Not vaccinated? You're putting others in danger, not just yourself.

A vaccine doesn't have to get anywhere near 100% protection to be effective - it just has to drop the viral coefficient below 1.