Referring to this post
Very tricky. I did some “professional librarian” digging using references from the original thread. I found several of the original thread’s comments (it had 85,000+ notes) and the first I found was this one: http://themetapicture.com/angry-scientist-finds-uneducated-internet-comment-and-delivers-badass-response/
From this, we can see that the original poster was someone by the name of “wonderbraforyourdick”, which is not the most promising of names for an immunologist and this is probably why the post was cut off as it was. Clicking on the name there indicates that the post was deleted and wonderbraforyourdick.tumblr.com brings up what looks like an almost entirely blank website. This path seems to be a dead end.
A bit more digging doesn’t really dig up much of anything. Mr/Ms Wonderbra didn’t seem to use Tumblr a lot before he or she stopped using it at all. The name does not appear on any other sites that I can see except in reference to that vaccination post.
I would guess that Mr/Ms Wonderbra either didn’t want any connection to the post or simply dropped out of Tumblr and may not even know how many notes his/her post got. It could also be that the parent of some kid saw the original posting and used the kid’s name to respond to it. In any event, the response seems to be very scientifically accurate, which only goes to show that you can’t always judge a person by his/her username.