It being agenda has nothing to do with being correct or not. I agree vaccines are good and should be given but at the time Disney was facing a PR nightmare (the debate was spurred by Measels in Disneyland) and Kimmel was used to spread that knowledge to those not informed. Having agenda is simply having a reason behind why you do something.
Telling someone even the most indisputable facts could be agenda driven if it were to serve me a purpose, say quelling fear (right or wrong that's still what it is). I don't disagree one bit with them wanting to get that message out but I most certainly can point to it as an instance where he did something beneficial for the larger company.