He's not anti vax. If nobody can challenge science, then it's not science.
Vaccines continues to help us, but that doesn't mean they are perfect and don't cause side effects on certain individuals. Hopefuly the future brings us highly personalized medicine instead of a 1 size fits all.
If someone has spent some time actually learning science then of course they can challenge science.
If they are a lazy halfwit parroting crap they listened to on the latest podcast (because reading is hard!)... no. Not so much.
(Well, it's way worse that that, but I didn't want to invoke Godwin's law.)
He is not "challenging science" with measured arguments and carefully controlled peer-reviewed research to back his claims. He's deliberately trying to silence science because of a completely unsupported brain fart.
And no, it's not about "timing". It's about spreading baseless FUD to discourage any form of vaccination, because he believes (with no actual evidence, and despite vast amounts of research to the contrary) that vaccination causes autism.