Look through a list of vaccine safety recalls. Here's a highlight of the big ones--this is the list that most vaccine hesitant people talk about when they discuss their issues with vaccine safety.
https://www.cdc.gov/vaccinesafety/concerns/concerns-history....
None of the side effects in that list took more than a few weeks to occur, and the majority them happened within a few days.
>HN is different than the comments section of a news site.
Tell me again how hacker news isn't reddit O user of 3 months.