When it comes to specialised knowledge, it is often beyond the means of novices to verify facts for themselves. In such situations the default position should be to defer to the consensus views of experts in that field. It is of course possible that the consensus of experts may occasionally be wrong, but it would be safe to assume that that would be the exception rather than the rule and that it is not up to the novice to identify such instances. In promoting these views it is sound to point out that we are not primarily expressing our own views, but presenting the consensus of professionals in that field.
A frequent hurdle with this approach is the popularity of conspiracy theories. One has to convince the conspiracist that it is extremely unlikely that nearly an entire profession would collude in some conspiracy. It is for instance nearly impossible for “Big Pharma” to mislead or bribe most members of the medical profession. Instances of misconduct may occur, but once again – it is not the norm and not for the novice to identify such instances.
Websites that generally contain the consensus views of the health professions include:http://www.nih.gov/institutes-nih/list-nih-institutes-centers-officeshttp://www.nhs.uk/pages/home.aspxhttp://www.health.gov.au/internet/main/publishing.nsf/Content/A-Zhttp://www.who.int/en/http://www.mayoclinic.org/
With regards to vaccines, the best advice will be found on such websites rather than on personal blogs of Facebook.