http://www.phac-aspc.gc.ca/im/vs-sv/vs-faq01-eng.php
http://www.vaccines.gov/who_and_when/
https://en.wikipedia.org/wiki/Edward_Jenner
http://www.historyofvaccines.org/content/timelines/all
http://www.health.com/health/gallery/0,,20476515,00.html
https://www.dosomething.org/facts/11-facts-about-vaccines
http://www.ncbi.nlm.nih.gov/pubmed/15568260
http://www.who.int/features/qa/84/en/
http://www.caringforkids.cps.ca/handouts/mmr_vaccine_myths_and_facts
http://www.businessinsider.com/why-vaccines-are-so-important-2015-2