Well, that would be why in order to make this into an issue people had to dredge up a single tweet from 2011 that simply read "no to mandatory vaccines." It's not like it's a serious issue of his campaign.
Are you serious? That link doesn't say anything like opposing mandatory vaccination as a condition for attending school. The whole of it reads:
"Should the federal government require children to be vaccinated for preventable diseases?
Gary Johnson’s answer: No."
Googling around I can't find anything that indicates that he opposes that, just that he doesn't want vaccines at the point of a gun.
his organization pushed for the passage of this anti-vaxxer bill in MS which did exactly that
http://billstatus.ls.state.ms.us/documents/2015/pdf/HB/0100-0199/HB0130IN.pdf
N ACT TO AMEND SECTION 41-23-37, MISSISSIPPI CODE OF 1972,
2 TO AUTHORIZE PARENTS OR GUARDIANS OF SCHOOL-AGE CHILDREN TO OBTAIN
3 CERTIFICATES OF EXEMPTION FROM VACCINATIONS FOR MEDICAL REASONS OR
4 FOR CONSCIENTIOUS BELIEFS IN ORDER FOR THE CHILD TO ATTEND SCHOOL;
Considering there is no such thing as forced vaccinations outside of this context, I am not sure what you think Gary Johnson would have been referring to in the Q&A you posted anyway. There is literally nobody out there arguing for vaccinations at gunpoint
http://www.latimes.com/business/hiltzik/la-fi-mh-no-obama-didnt-pander--20150202-column.htmlIncidentally, my googling did turn up this.
http://www.theatlantic.com/science/archive/2016/08/an-anti-vaxer-in-the-white-house/493916/