Comment by summerlight

Not sure if everyone has read the actual policy (https://support.google.com/youtube/answer/11161123) but for those who hasn't:

    Don’t post content on YouTube if it includes harmful misinformation about currently approved and administered vaccines on any of the following:
    * Vaccine safety: content alleging that vaccines cause chronic side effects, outside of rare side effects that are recognized by health authorities
    * Efficacy of vaccines: content claiming that vaccines do not reduce transmission or contraction of disease 
    * Ingredients in vaccines: content misrepresenting the substances contained in vaccines

Also, the policy states some exceptional cases such as countervailing views with a support from medical experts, firsthand experiences, etc.