Where has it gone wrong?
“We did not call into question the integrity of The BMJ’s story, only the comprehensiveness of it. That’s the point of a ‘Missing Context’ rating.
The BMJ article is being used as evidence of Vaccine Conspiracy theories, it's not like the warning is on the Article, it's where it's shared on Facebook and the missing context label is relevant in that context. A context where the vast majority of people viewing the facebook posts will not understand the BMJ may cover a sub-topic where the results do not reflect on the outcome of the parent topic...