People seem to assume that all doctors are roughly equal, or at least meet some baseline level of competency. I'm saying based on my experience in the engineering world and my first hand experience with doctors I don't believe that. So I'm saying that just taking someones word for it because they are a doctor is naive. I've lost track of the number of times I've been told totally nonsensical things by doctors that were just not sound advice which I confirmed by seeking another doctor's opinion and in some cases because what they told me to do made me sicker.
You might not say it, but you'd probably think, "really? You probably don't know a function from a hole in the ground."
Personally, I can't tell you what all of my organs do, much less what can go wrong with them, much less how that should be treated. I'm sure there are incompetent doctors, but I doubt there are many less competent at medicine than I am.
Luckily this isn't relevant to vaccinations because we're not relying on what one person says, but on an accumulated body of research.
Vaccination for varicella is tricky - if you're going to vaccinate against it, you need to vaccinate hard. It's a great working example of what's known as the "Paradox of Moderate Infection Control" - getting a handle on it just a little bit will cause worse outcomes than if you did nothing at all. The WHO then, making recommendations for the entire world, logically favors a single "Do it and be done" shot that piggybacks on their incredibly intensive campaigns for MMR vaccination.
In the U.S., a varicella vaccine is a co-occuring part of the recommended vaccine schedule. It's a question of one shot or two, and managing slightly worse side effects for the MMRV vaccine, and thus absolutely sensical to leave it to the clinician and parent to discuss, because the likelihood of the child getting one and never getting the other is quite low, it's just a question of how.
It's also a conversation that's pretty orthogonal to most anti-vaccine discussions, so it feels like a bit of a red herring.
They're done by panels of doctors who are experts in that field, and the supporting reasoning is extensive and the result of many, many peer-reviewed studies.
I'd certainly trust a random doctor's medical opinion over a random programmer's (my own). And I think a doctor should trust a random programmer's opinion about software over his/her own.
In both cases, the solution is to find a reputable practitioner, not substitute an untrained opinion for a trained one.